Should I mount a projector right side up or up side down?

I have an Epson 2100 and a shelf right above my window opposite the wall where the screen is hanging. If I place the projector right side up, the image is very high off center and requires a good deal of lens shift and keystone to square it with my screen. However, from what I’ve read it seems like placing it upside down will give me more downward vertical spacing and make the image much easier to center. In other words, do projectors naturally project higher than the lens itself? and will flipping it upside down place the center of the image lower on the screen before lens shift is applied?