The only larger group ride I do is weeknight worlds a couple times a summer. In that, definitely in front 1/3 or in the rotation or in the break. The back 2/3 always is dropped by the break of 3 to 6 folks. Then it's either the pro or cat 1/2 guy that "makes it" or a bunch sprint.
Otherwise, I only do group rides with my teammates doing a very nice and tight formation. Either rotating constantly or taking turns or planning a little leadout train for a townline. Max of 6 of us then. In those, everyone pulls but is free to sit out a rotation or few.
I'm not a big fan of the cluster F 18mph critical mass roadie group rides where folks wear headphones or wander all over the place like a flock of chickens.