All projectors that I know of have zoom capability. What I did when I first got into the projector world was calculate the approximate top and bottom of the image at the throw distance I would have. Some of it was also just holding the projector by hand, getting it close to level, to see where the image fell on the wall, which determined how high I would mount it.
After mounting the projector, I went through the fine tuning process of getting it perfectly leveled such that I had a straight and square image on the wall. THAT result then showed me what size screen frame I needed to make, and the area of my wall that I needed to paint with screen paint mixture.
I dunno, maybe I did some of that a little backwards from what others have done, but it worked well for me.