I am not familiar with that model, but if you were talking about an Infocus X series projectgor, I would say that you had a bad light tunnel.
If that is the case with yours, the only cure is to repair or replace it. Since I don't see that parts are available, that leaves repair of the bad part. And that is something that you are going to have to do.
The light tunnel is a small, 4-sided mirrored tunnel that is glued together. In the Infocus projector, one side of the mirror would come unglued and that side would collapse inward, darkening that side of the image.