I've always bottomed and have never topped because I think my 5inch cock is too small for topping. For those of you tops, is there an actual size necessity for effective topping?

I feel 5 inches could get into a guys ass and thrust a little, but there isn't enough length for me to actually get the full motions down.

Again, I've never done it so im totally speculating. Am I on the right track or totally wrong on this?