Former New Zealand cox Cotter, while maintaining an all-encompassing view of the success, singled out the silver medal-winning pair of Rebecca Scown and Genevieve Behrent, the lightweight four and the women's eight for special praise.
Scown and Behrent, who also double up in the eight, gave reigning Olympic champions Heather Stanning and Helen Glover their toughest battle in a while, forcing the British pair to produce the leading World Cup time of the year.
The lightweight four of James Lassche, Matt Dunham, Alistair Bond and James Hunter, repeated their win at the Lucerne regatta at the end of last month.
Dunham has done a fine job filling in for the injured veteran Peter Taylor, who is due to return to activities in the boat on Wednesday after a niggling back complaint.
Cotter said, as well as the four had done with Dunham in the No 2 seat, Taylor would go straight back in. There's no chance of making Dunham's role permanent.
"Peter is selected, it's quite simple. He's fully fit now, 100 per cent, and he goes back in the boat. That's just the way it is," Cotter said.
Taylor has been training in a single but wasn't race fit, so sat out the Poznan regatta.
"Matt did a great job in both regattas and reserves are an important part of the team, and you need them in Europe."
The women's eight swapped Emma Dyke from the No 2 seat up to stroke, swapping with Scown, and it worked a treat, the crew bossing the final from halfway.
The move lightened Scown's load, as she was in her second final of the day, but Cotter said it also came down to coach Dave Thompson working to get more boat speed.
"It's a coach thing, the feel and what you see in the boat. And I'm sure it's taken pressure off Rebecca," Cotter said.
The squad now split into two groups, the crews overseen by Noel Donaldson and Calvin Ferguson heading to Sursee, near Lucerne, those in the hands of Gary Hay, Thompson and Dick Tonks to Slovenia.
They are split along training lines, for example the women's eight and lightweight men's four can produce comparable speed, and both are coached by Thompson and Hay; the men's pair and double scull, coached by Donaldson and Ferguson respectively, are also able to train productively together.
There are no more regattas, but the focus is on a solid five-week training block, fine tuning for Rio.
Cotter also pointed out Rio will have more issues for the rowers to deal with than in Poznan.
"It'll be a different environment, with all the other sports, and different things happening with transport along. In Poznan, our hotel was on the 1000m mark so we could walk to the boat park.
"(In Rio) we could have a 45-minute ride on a bus, or an hour 15. So we've just got to roll with the punches and stay relaxed. It's still a 2000m course, but different things happen."
