toes jamming

I have heard a lot of people complain about jamming their toes in closed toe bindings and I was wondering if that happens when bindings are too big or when they are too small or both. I want to get some Ronix closed toe bindings and I wear a size 12.5, so if I get the size 12 it will probably be really tight and if I get the 13-14 it will be a little loose, what do you guys think are the drawbacks for me to get them too tight? And what about too loose?
Thanks