There are other variables. In some groups riding a double pace line, the two pullers end their pull synchronously, requiring some communication about when to be finished. There are other double pace line rides when people finish asychronously.

When I was in Germany, I went on a Berlin Rapha Clubhouse ride that was the most regimented ride imaginable. Double pace line, all pulls ended synchronously and the pulllers went all the way to the back. Consequently, the person next to you remained your partner throughout the ride. Actually, pulling in that scenario just felt like work. It didn't have the joy that motivated my OP.