Hmm... yeah, I can definitely see you going for that there. Hm...
Well, you've clearly got the right idea - the sharp, broad jawline - I think the trick is just the perspective, maybe? I tend to go for the same sort of thing, and
this
◊ is my result. I also use a convex muzzle as a default for ponies that are supposed to bigger, fuller, more masculine, etc. Really, all you can do is what you have done - broad chin, sharp edges...
Actually, for an interesting point of comparison, here's
Bruce Willis
◊, and
his daughter
◊. Notice how they have the same jawline, but it looks better on him(Tastes notwithstanding)? It's the fullness of it, the way it sort of flares out, that makes it looks extremely masculine.