I don't think the 3 inches are as big a factor without a deep substrate ?
For me if I can't reach the back bottom without 'climbing in' it is too deep .24 inch deep tanks are my uncomfortable limit .Especially on 24 in wide tanks .
I have to 'climb in' my 180 to move a large rock or such it seems sometimes ..
For me climb in means have my waist close to even with top of tank to reach in ..Hoods and such add to the difficulty IMO ..