McColl started mentoring McCartney seven years ago after she popped along to one of his trainings as a 13-year-old high jumper.
The 34-year-old exudes calm. His physique suggests a man who seldom fraternises with the products of a deep fryer.
His perma-tan hints at a life spent outdoors. His gaze is penetrative and bears the intensity you'd expect from a former gymnast capable of executing a Maltese Cross on the rings.
He speaks in measured sentences, reaffirming the belief in his charges, many of whom used poles bought out of his savings so they could continue in the sport. No wonder the disciples are flocking.
"Our club poles were old, which meant there was more chance they could snap," McColl says of the early days.
"With pole vaulters trying to build confidence as much as technique, I made the decision to invest because initially there was no opportunity for funding.
"I acquired 170 poles, ranging from 10-foot to 17-foot, that's not quite a full set; we're working towards that."
McColl estimates each pole cost $500-$1000, making for a significant outlay while he worked as a builder.
"Post-Rio, Athletics New Zealand bought my poles off me. It's a great step forward, and a bit of appreciation for what I'd done - it has been tough. They have also committed to a budget to purchase more.
"There's the possibility of getting a second set so when athletes go away you can fill the gap. The German programme, for instance, would have about five to six sets of poles because there are so many athletes at that [elite] level."
Athletics New Zealand will pay through their core high performance investment. As a "Tier 1" sport, they are guaranteed funding for four years, starting with $2.6 million in 2017.
Technical nous will also be required with the purchase to work out how many carbon or fibreglass poles to acquire.
Carbon poles can be used more aggressively in the box, but unbend faster on release, making precision paramount.
McColl swayed towards sports coaching in his late teens. He has spent three years tutoring gymnasts, and 12 years in track and field, a sport where he also excelled at sprinting and long jump.
He describes his athletic career as "crashing down" after a pole vaulting accident in his early 20s.
"I landed in the box, tore a tendon in my foot, and didn't vault again until the following national championships. Eliza is jumping higher than I was [McColl's personal best was 4.70m]. At 23, when I stopped vaulting, my body felt smashed.
"I was fascinated by it, because it was the extreme sport of athletics. As soon as I got a pole in my hand I was hooked. It's not as hard as it looks and I love seeing the smiles on the faces of those learning.
"It's one of those events where I always believed New Zealand would be world-class."
McColl spends six days a week monitoring his stable.
"The group is tight; a bunch of incredibly smart kids who like seeing each other succeed. At practice on a week day they're out there with the music cranking, pushing each other."
Successful vaulters tend to come from polar opposites on the athletic spectrum - sprinters versus gymnasts - although most champions are a hybrid. Sprinters, more like McCartney, know how to best transfer kinetic energy on the runway into power via the pole.
Gymnasts, more like Russian world record-holder Yelena Isinbayeva, have a better understanding of their body position as they levitate in an "L" shape through the air.
"I've done a lot of study and surrounded myself with good mentors," McColl says. "Steve Rippon, the Finland national coach, was big in my early development having spent a lot of time with the Russian and European-based coaches.
"Katrin Klaup, my fiancee's mother, is a combined events coach. She has helped me programme my pole vaulters to be more like those athletes; running, jumping and throwing a bit."
McColl has added technical innovations to the New Zealand scene, like a downhill runway to allow athletes to train at higher volume.
"The theory is you can get up to speed faster off a shorter run-up. A top male vaulter off 18-20 steps can create that same effect with 8-10.
"It also means you can fit 30-40 jumps in a session. Athletes get through far more work. Volume and quality is important. You can practice technical skills to a high level with less energy and a lot of repetition."
However, McColl is concerned pole vault has a limited development arm in schools.
"I learnt pole vault too late. I was 21 when I started, you need to be learning at 13 or 14 [like McCartney]. I was doing gymnastics until I was 18 or 19. King's College is the only facility I can think of with a pole vault [set-up] on site.
"It might depend on getting the right health and safety [practices] but I would love to see it more widespread. If teachers and coaches were at a high enough level it would boost the sport, because athletes could come to me with some degree of development. I don't talent ID. I take whoever comes along."
McCartney and McColl will be based in Germany for the start of their Northern Hemisphere campaign.
They will work at what McColl considers the "best facility in the world" in Leverkusen.
Pharmaceutical giant Bayer is based in the town and sponsors the venue which McColl estimates at "10 times" the size of the Millennium Institute.
It incorporates two indoor and three outdoor pole vault pits and an army of biomechanists.
The duo will travel to Diamond League meets in Oslo, Stockholm and London, after McCartney yesterday won bronze in Rome with an impressive season-opening effort of 4.75m. The highlight might be visiting Jockgrim in Germany.
McCartney will compete at a boutique meet parallel to the local football pitch where a crowd, inspired by beer, get progressively boisterous as afternoon fades to evening.
The pair will return to London for the world championships in August. The aim is to have McCartney at a full run-up of 16 steps to maximise her power.
She competed off 14 at Rio and reached her personal best off 12 in February.
"Who knows what she can jump this season with bigger poles and more confidence and consistency?" McColl says.
McCartney is the pioneer among McColl's troupe of human slingshots. Her career prospects are rising as fast as she does, when planting a pole between foam mats. Rio was just the fifth time women's pole vault featured at the Olympics.
The only previous New Zealand female to be selected in the discipline was Melina Hamilton at Athens in 2004.
"It'll be easier for those after Eliza, because they know there is a pathway," McColl says.
"She's an incredible role model they can talk to about training, competing, managing sponsors, work, university or how to balance those things.
"In making the transition [to being an Olympic medallist] she probably struggled with the attention initially, but not in a bad way, it was more of a surprise.
"Walking down the street she gets noticed and she gets asked for selfies and autographs in restaurants. There are also letters galore, particularly from Germany."
McColl knows change is likely now McCartney is a known quantity.
"She'll go into events with expectations. You wouldn't know that in training at the moment; she's bubbly and happy. She needs to have fun, but still handles herself with the utmost professionalism."
The essence of McCartney's success has been an impermeable countenance at big events, such as the Olympics, where the crowd can be your frenemy.
"We had good feedback from the Games, people admired what they saw," McColl says.
"When you go to big championships you see a lot of serious faces and people crashing out without fulfilling their potential.
"It's noisy in an Olympic stadium and coaches are far away in the stands. Better vaulters are the ones who work things out for themselves. A coach can tell you what it looked like, but they have to feel it.
"It's important not to set a benchmark for Eliza. If she wants to be the best of all time, we don't want to work to barriers or goals."
