Under normal circumstances I'm not that fussy when it comes to bait size. Anything around the 14-18 mm will do me fine. I rarely use chops, and I rarely use crumb. I might use smaller baits on a very, very hard/clean substrate (spotless gravel) but tbh it's been years since I've fished spotless gravel. I might use bigger baits if bream become a major issue. Like I say, not fussy really. I think where you put it is what really counts.