I've never really cared much about the bottom's cock size. But I do have a strong preference for bottoms who get hard while getting fucked. I like fucking to be a mutual, interactive experience when it's one-on-one and I don't enjoy it as much when the bottom has a flaccid dick the entire time. Regardless of cock size, love it when the bottom is rock hard and edging while he's getting fucked and ready to burst as soon as I breed him.