The Paulistinha is (was?) a Brazilian-made version of the Taylorcraft and so, yeah, definitely not designed for aerobatics, though the smaller version of the model can definitely do all the basic aerobatic maneuvers.

If you look at the photo above you can see that the "vertical center" of the firewall would be below the hole. The marking lines for the gas engine cross just above the hole. Visually, it seems like having a radial centered on the firewall so that the cowl extends equally above and below the nose would look "least awkward." Bear in mind that the main goals with this model are 1) to have a "test bed" for the engine and 2) to get some experience flying, handling, transporting, storing a large model.