One thing to consider....there is the minimum sized baffle that just doesn't allow any direct stray light to hit anywhere on the focal plane (and AT the focal plane)...now since most eyepieces project inside the focal plane..
And this was illustrated above in my figure !!
Now, it occurs to me that once one defines the maximal stray-light-free-field and uses a Paracorr 2, the only other dimension needed is the distance from the light-entering-end of the Paracorr to the shield itself ! Everything else is simply linear math.
Let us postulate that we want a 46mm focal filed free from stray light (after Paracorr). Before the Paracorr magnification and change in focal plane position, the size of this field is 46/1.15 = 40mm which is 20mm (0.787") off axis.
Using the same figure as above:: the position of this uncorrected focal plane is 3" + 9mm = 3.354" from the light-entering-end of the Paracorr 2. The distance from the Paracorr to the light shield is 21.2" for a total of 24.554"
The aperture of the light entering end of the Paracorr 2 is 46mm (= 1.811"); so now we have a complete piece of geometry.
The "run" is 24,554 and the "rise" is 0.787 + 0.9055 across the Paracorr distance of 3.354 distance
and we are looking for the rise if the distance were 24.554 !
1.6925 = 0.787 + 0.9055
12.390 = 1.6925/3.354*24.554
and all we have to do is subtrace the originating offset (0.787) and we have the half diamete of the light shield.
11.60 = 12.390 - 0.787
so the light shield needs to be 23.20" in diameter.
You may not need a 46mm illuminated FoV (only the 41 PanOptic has a field stop this large (reduce as desired) and in my case since this is an F/3 the field stop of the 21E is only 36.6mm allowing the slight shield diameter to shrink to 21.1"