The smallest i have needed has been 2" pads on my rotary and they work great. Just for giggles i fashioned a 1 and 3/4" bp out of an old DA backing plate and tried it to finish out after my rotary. I didn't like it and know exactly what Mike's talking about with the "tippy" analogy. I will say that i tried it and didn't like the feel of that small of a pad on my PC but you might feel differently.

I use the hand method to get right up to my taped edges.