What I'm getting at is that your nose starts between your eyes, then it just out more and expands wider the lower down the face you go. Well, there's no possibility for a nose bridge for monoeyes. Their noses are going to be small bumps just below their eye, and their ability to breathe through it is going to be severely limited. In fact, they'll be mouth breathers and any sense of smell for them will be reduced as well since the large eye will take up space for a more developed olfactory system.
Monoeyes already look strange. The weird nose structure they'd have would just add to that.