At the cameras.cam settings i am using setting the marks at 12 pixel seperation gets it right on target in game.

Getting this figure and the cam settings took a whole lot of loading/reloading the game to check distant differences with different angles.
Wish there was an easier way to check stuff in game.

If you want to get the spacings download the update to my mod and use the mark distances as I have them set.

How big is your viewable area Emtguf ?

We would like that as big as practicaly possible so the resolution of the scope is as big as possible.

Ill try later today to check all the above posted attempts and calibrate a camera.dat for each.