It's the same as it would be without a mirror kit.http://www.projectorcentral.com/3M-X90-projection-calculator-pro.htm
With a standard lens, 12'1" to 14'7". You just add the distances that the mirror folds the pathway.
So, 6' from projector to mirror, then 7' from mirror to screen = 13' which is perfectly fine. You just have to make sure you are in the right range, and that you are using a standard lens.
Their short throw lens only allows it to go as close as 9'10" for that same 120" diagonal, but has greater range, so 9'10" to 15'11" is possible with their 'short throw' lens option.
But, that distance stays the same with or without a mirror.
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