Not sure what to tell you, you shouldn't be getting hot spotting with a gain of 1 screen. I doubt it is the project or doing it. This is the third projector I've used with this screen(1 high end Barco CRT and 2 Sony SXRDs) and have never had any hot spotting issues, which is one reason I bought this screen is because people said it had no hot spotting problems.
If you can take your projector over to someone else with a setup and try their screen. I've never heard of any complaints with this projector and hot spotting.
Is your projector new or did you buy it used? I'm guessing it was recently new at only 400hrs. I would check out how it has been setup up because something does not add up here. What are your setting at?