So my throw ratio with an Anamorphic lens would be 1.8x? The RS50 supports 2.0x is this acceptable or will I end up with noticeable pin cushioning or softness around the edges?
I want to make an informed decision on scope screen size and mounting distance before I commit to the install
Your throw is indeed around 1.8, and your pincushion will be 17mm, or 1.3% of the screen height. Not bad, OK etc.
But at the longer TR of 2.0 that you mention, the pincushion/height percentage is 1% (about 13mm): much better, less noticeable than 1.3%
My advice: go for TR=2 if you can.
In the end of the day, if they are using a fixed 1.33x lens, then 16:9 + 1.33x lens is 2.37:1 regardless if the screen is 2.35 or 2.40. The difference to perfect framing is just a few percent of over scan.
Few 'scope movies are 2.37. Most are either 2.35, 2.39 or 2.40. What I do with my HD-100 is to use the MASK menu function to digitally clip the edges by 2.5% (5% also available, but this is too much). I believe this function is in all JVC projectors.
That way all four formats from 2.35 to 2.40 will fit into the mask (with some minor cropping around the edges). I then zoom the projector just a touch, to fit the width of the digitally masked area into my 2.37 screen. The height automatically fits. That way I never have to tweak the zoom to get rid of unwanted black areas across the top edge of the screen when showing the wider ARs of this 2.35-2.40 range.
The small amount of action you lose around the edges is neither here nor there. Directors shoot their movies for 2:1 cropping in commercial cinemas anyway, so cropping back a couple of percent is well within their target range and worth it, IMO. for the release you get from worrying about the last few millimeters of action you were never really expected to see anyway. You can use fixed masking too, which is another advantage: it's cheap.
BTW, I know this is heresy, but it works for me. A great movie is still great cropped by 2.5% all around. A rotten movie is still rotten, no matter whether you see all the action or not.