Personally, I think that as long as one's viewing position (head) is at the center of the screen or below, in the vertical direction, and the projector is placed above, in line with the top of the image,
then all this should work out fine because you're never in the light path anyway.
The advantage of this is the projector can be either just put on a high shelf or be ceiling mounted up-side-down for the same result. I can see how this can work well for different set-ups.
Definitely agree that this all should have been worded differently though.