Yayyyy it works

and even better than expected....I discovered something interesting in the way:
When opening in S3D editor the scope optical parameters I noticed an angle of aperture of 57 (degrees?)

instead of the 32 the historical scope had. Re-scaling that 1.6 times down gave me a new value of 35,79 degrees -which also matches more or less the historical FOV- and as a result:
- The zoom (Even if kept at 1,5x/6x) effectively is much increased, allowing for much better perception of details
- The marked lines went out of the screen

and can now be replaced by an Alpha channel image conveniently placed in the Periscope TGA
- The in-game built stadimeter still works as intended -as you could expect-
It seem to be a win/win situation

but I'm going to test what happens with an exact 32º field of view.