It's simple. The full-scale airplane had a monsterous radial engine on it. Our model airplanes are so much more efficient than some of the older full size engines that it's ridiculous.

Look at a P-40. Notice how much of the nose is filled with engine on the full-scale version compared to a model. So it's really not unusual at all to have to add a lot of lead to the nose - especially when dealing with a scale model