Bigger size causes more problems, but I belive that ideal size balancing appreance and practicalness is still bigger than Rainbow Dash`s (and defenitely smaller than Fluttershy`s) current size. It also depends on a girl`s own will, motivations and so on.
ok so at my school there is a boy in sixth grade and he has very slow reactions apparently and I heard he was playing tag and he tagged this girl's ya know and his hand was on her chest and she just froze there in shock. when he noticed what he was doing he walked away and can you guess what he told his friends????