To show more clearly what I meant:
I wanted to project onto the lower part of the wall, but I can't tilt the lense up or down and I can't place the projector closer to the ground neither, cause my couch is blocking it, so I had to put stuff under the projector to make the lense face downwards. I probably wouldn't have this problem if I could attach it to my ceiling. But this can only be a temporary solution. Anyone have any idea?
I want to project it on the lower side of the wall because of this:
The right side is not straight, this make it hard to put a screen on the wall. I've measured the size I want my screen to be and that means I need to project on the lower side of the wall,and tus I need to tilt the lense downwards, but I can't.
Here is the link again for the HD131XE: http://www.projectorcentral.com/Optoma-HD131Xe-projection-calculator-pro.htm
The calculator shows you the only way the projector will work. Each projector is made differently. Some can shoot at the screen from a spot in the middle of the screen and others cannot. This projector must be mounted above or below the screen. If that isn't possible for your setup then you need a different projector. The calculator must be followed. The reason why it needs to be followed is the use of offset. Here is an illustration of offset.
If you tilt the projector in to make it fit and then use keystoning, your focus and geometry will be a mess.
A plasma flat screen might work better for you.