I don't tend to weigh my prey until I tried to look at f/t for this years for sale babies. Based in the 10% thing what I feed is huge! As you said in the 20-30g range. I actually prefer the way I did it last year tho, typically my babies gain 80-130g a month. I had no issues and as long as its not too big I don't know of any reasons not to feed larger prey.