No matter who is in front, that rider will always feel pressure to set a good pace. The rider in 2nd position will do everything possible to keep the wheel of the rider in front. The rider in front will sense the rider in back of him and feel the need to pick up the pace. The rider in 2nd position will again try to match that pace and keep the wheel. This cycle continues well into the ride until everyone is riding at their limit and bleeding out of their ears.
It's what makes a group ride a group ride. Even though it hurts. I look forward to it.