I don't think this will work.
Throw distance is measured from the front of the projection lens to the screen, not from the center.
So, with the center of the projector at 21" and a distance to lens about half the depth of the projector, you only have 16" or 17" from the lens to the screen.
While that would be a 43" to 45" diagonal, about the same size as a cheap flat panel television, it is outside the range of what that projector is designed to handle.https://www.projectorcentral.com/Ricoh-PJ_WX4241N.htm
Ultra short throw projectors, unless they use extremely high end optics, are extremely size limited with poor focus outside that range. The Ricoh you have calls for a size between 60" and 400" diagonal. So, it can go big, but it can't go that small with the optics which are in use. Typically closer to 100" to 120" diagonal would be common in a classroom/business environment.
Using the calculator: https://www.projectorcentral.com/Ricoh-PJ_WX4241N-projection-calculator-pro.htm
It would really call for the projector to be about 3'4" lens to screen, or about 4'5" off the wall to the center of the projector for a proper 100" diagonal.
I would look for a different mount which has more reach, or mount directly to the ceiling using a Chief CMA440 and a RPMAU mount.
For short throw, you can also look at the Chief WP23US. This model is pretty much right on target with a 56" wall to center distance. My calculations above shoot for 53" for a 100" diagonal, so this would be perfect.
Be aware, many Amazon mounts are not UL listed and may not be used in commercial applications. Chief stuff is pretty much the gold standard in the commercial space for hanging projectors.
[Edited by AV_Integrated on Sep 30, 2020 at 1:03 PM]
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