Hi, yeah the throw distance is lens to the screen. If you absolutely want the screen "THERE", hang the screen temporarily and then you'll need to start doing the math, or using the throw calculators that are available on the web. If you get a modern projector with a generous Zoom ratio and lens shift, you'll have a much easier time placing the PJ.
However the other part I don't understand, your photo I don't quite get. Perhaps not zooming in so much so we can see the walls, etc....
If you don't get a projector with lens shift, be mindful of whatever OFFSET that projector you choose has....that will be how high above the centerline of the lens the actual image gets projected. My Marantz PJ has a very low offset, the image on the wall starts at whatever height the centerline of the lens is at. But my Optoma has a higher offset, it projects its image higher than the centerline of the lens. Again, this only comes into play if you buy a PJ that does not have lens shift.
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