There are limitations beyond the first 50 feet: He can't use his semblance on anything outside of it, and he still needs to see it first before he can start affecting them. Things within the first 50 just means he can control them while both fighting and moving without worrying about his R-Types just dropping out of the air because someone is whaling on him. Things beyond that are harder to control especially if there's something in his face.

Plus his semblance, currently, is very reliant on sight. If you say, put a blindfold on him, his semblance is essentially disabled. He can't even use it in the dark. Only his R-Types he can use without looking at them (Otherwise he'd never get them out of the Kingdom), and even they still need to be within his first effective range.