Because of the REALLY bright bulb that will damage your eyes? (excited) XD Much less of a problem with ultra short throw, as the screen AND projector are in front of you! ;)
Once you've got a projector you'll NEVER look back...
You can check the screen size possible from any distance for most projectors by using a projector calculator like this one on the projector central review site. https://www.projectorcentral.com/projection-calculator-pro.cfm
Wow, that's incredible how you're getting an 100" screen for that distance. I've ordered a BenQ W2700/HT3550 for my first projector. I've got a 8ft throw distance but I think I'm only going to be capable of a 90" screen. Fingers-crossed I'll get it to 100". Really looking forward to seeing how good movies and games look on a projector.
I made a 100 inch screen Throw setup is 120cm away I think roughly.