that explains the FOV in the virtual image, but not the size of the virtual image ...
eg. take an SLR with zoom lens, when you zoom, the FOV (magnification) changes, the size of the virtual image doesnt.
Zoom/power and FOV do not exactly make sense when translated to a computer screen because moving your head closer and farther away changes zoom.
When dealing with a computer screen you really only have a field of view because lowering the field of view effectively zooms in.
Hence we choose the best zoom/fov ratio and use that as a base to have a circle touch the top and bottom of the screen.
After which sights will the same power will be the same size on the screen, but as the sights FOV decreases the circle will become smaller.
So the objects on the screen will be the same size for any 6 power sight. But the circle size will vary with the sights FOV.
HiTech