Yeah, the standard posts are only about an inch long and on an LP, with a steep-ish neck angle, they barely go through the maple top. Whereas a longer post would go right through the maple and into the mahogany.
From what I read it's probably not worth making them too long, it gets increasingly hard to screw them in and they might snap. The ideal seems to be about 1.5", with 0.5" of that above the surface, and the key is supposedly to screw the post in until it touches the bottom of the hole (although I doubt the holes are all drilled to a uniform depth!)