Oh, Sian, the beauty of a roundhouse kick is that it will fell ANYONE. Actually, in practice, I quickly won against a guy with 6 inches and 100 lbs on me. It's all about leverage and speed. Speed with beat strength every time, you just have to build the muscle memory.
See? This right here is why I prefer attacking from a distance. I like to measure my strikes by things like "kilometers" and "megatons".