i have used a wide grip on bench press with my index finger on the rings like you are talking about, but it was uncomfortable and i felt like it put too much stress on my shoulders so i have moved my grip in to the point where my pinkies are on the rings. with a slightly closer grip i feel a lot more comfortable and i can actually put up more weight.

on military press i like to take a slightly wider grip with my middle finger on the rings. for whatever reason that just feels the most comfortable for me.