the correct size or a larger one?
order the correct size– the additional breathing room makes it so much more comfortable for them, even in the hot weather. you may find that you can use a closer fit, which will help the muzzle stay in place better and make it harder for them to get through the cracks on the side. i would think you could use the larger size also, but i would be a bit concerned it would be too loose and easy to twist around to the side corners.
the big advantage to this design is that the plastic can be readjusted or bent as many times as you 