Interesting. I’ll try to duplicate your setup as much as possible and post the resulting images from my Dell S300’s. I also have a Hitachi A350.
My experience is that the A350 has edge blurring due to angle of entry in the rear-projection material. For that projector I used a thinner rear-projection material (7D513) or thinner.
With the Dell projectors, I do not have this issue. However, the throw distance is fairly short and my angle of entry is much closer to a straight on projection.
I’d be curious to know if you have the same issue using your surface material in a straight rear-projection (no mirror) configuration. Obviously this doesn’t work for your slim table build, but it would settle the issue regarding angle of incident versus quality of material.
Again, as I can, I’ll run these tests on my end with my equipment and attempt to post the results. My lab space is currently configured for another project right now, so I may not be able to generate results until this weekend.
Update: also, I failed to mention how your setup is looks great! I love the use of maytec (not 80/20 right?) aluminum extrusions. These products are amazingly good at accommodating the multi-touch requirements.