Most people like the ratio of viewing distance to screen-width to be between 1.25 to 1.50. I love the ratio of exactly 1.35x. That is, if I am sitting 120 inches / 10 feet away from the screen, then I want the width to be around 120/1.35 = 89 inches / 7' 5". It is different for every person.
This projector has a throw ratio of 1.55 which means you should get the width of 69 inches from 9 feet / 108 inches. So for me, I would need my seating to be at 69/1.35 = 51 inches / 4' 3" to get an immersive experience. Try standing at that distance from your wall-screen and see how 1.35x feels to you and also notice if you have to rotate your head too much.
Also, can you measure and let me know exactly how many inches higher up the projector needs to be kept from the bottom of the projected screen? I forgot to measure that when I had a unit.