I was *lucky* enough to witness my d'Anvers roo (1lb) with my standard BR girl.. LOL! Well, he grabbed her head.. and made contact somewhere mid-wing. It was pretty pathetic.. and I think I laughed the rest of the day.
But now he seems to have changed his technique. Last attempt he didn't bother grabbing her head, and seemed like he managed, or at least came close. Where there's a will, there's a rooster willing to figure out HOW.
I also would be worried about a standard sized roo with bantam girls. I'm sure it's possible.. but there is a squash factor there.