Here is the calculator on that particular projector. It looks to be a long throw not short though.
http://www.projectorcentral.com/Acer-X1 ... or-pro.htmI use Rose Brand Tendo screen fabric on my setup. I don't really like it though. It bows forward under tension several inches with a screen my size.
Ideally you want to find projectors with a lens throw between 0.72:1 and 0.49:1. 1:1 lens throw means that for every 10 foot distance the projection width is 10 foot wide. For example with my 0.72:1 Optoma GT720's for every 7 foot I get a 10 foot wide projection. A 0.49:1 projector would only use 5 foot distance to throw a 10 foot wide projection. The shorter the lens throw ratio the closer a projector can be to the wall to make the same size. Also the shorter the lens throw the more you need to worry about the screen radius. Really short lens throw and really small screen radius makes for a lot of distortion that needs to be corrected. It's also why I don't use 0.49:1 projectors on my current screen.
There are no hard set rules or guide to this stuff though. It's mostly been made up via trial and error with customer experiences over the last 5 years. I used to believe in triple-projector no smaller radius than 6-7 foot, but now I'm using dual-projector and 5 foot radius. Through both of those I still believe 800p projectors should not project taller than 60" or the pixel size gets too ugly. My main thought process on dual projector is less hardware to deal with and less cost, but with you needing Nvidia 3D Vision it'll require 3 projectors.
-Brad