What are the benefits of mounting an engine above the fuselage?
It's strictly to stay clear of spray in seaplanes, or because the engine was tacked on as an afterthought for some reason (like a motorglider conversion) and that was the only place to put it.
There aren't any aerodynamic benefits, or you would see the configuration on landplanes.
You've increased the frontal area by having a big pod sticking out.  The high thrust line wants to pitch the airplane over, increasing tail trimming forces required to compensate, and hence drag. There there are the undesirable handling qualities, mainly a strong pitch down tendency when you add power quickly, and worse, a pitch up tendency when you remove power quickly, which can get the unawares into quite a lot of trouble.
So to summarize, sticking an engine there is only done when there's nowhere else to put it.