In fact, F3C flying requies you to be at about 5 meters at some moments. That is 15 feet. And many F3C people are flying 90 size stuff. And it seems usual to hover at about 2 meters (6 feet) when testing is done in the start box. I have a 50 size but still I think 5 meters is pretty close. But what do you do if you like F3C flying? You need to be close for precision flying anyway, this flying is about movements in the centimeter range