I have on my 16.1 who is very long bodied, and it looks fine. Its so much nicer having a 16.5" saddle than one that feels like a basket if thats what you need, I really wouldn't worry about it. If I get a bigger horse, I will always use a 16.5" saddle. I might even consider a 16".
I use a 16.5" on a long backed 16.1hh. I also have the saddler coming and fitting a new 16.5" on friday. I'm 5ft7 and weigh just under 8 stone, anything bigger and I'm slipping and sliding all over lol