He might still be injured, but it's also true that some people are just crap at jumping. However, just because you are tall doesn't mean you thrive off the high ball. Higdon's strengths lie elsewhere. He is a bit like Porter - a good link up player, a natural goal scorer and, by SPL standards, a wee bit slow.
You only need to see how many he banged in for a poor St. Mirren team to realise that he can definitely cut it at our level.
From the highlights and live games I have seen, he does seem to be isolated far too often. Whether we are pressing or playing counterattacking, he needs support.