Hi padaro,
I see no one is having a go at this, and I'm by no means the expert, but I'll make a start and let someone correct me.
The higher the scope is mounted from the center of the barrel, the more it interferes with the visual trajectory of the projectile.
Obviously, when the barrel and scope are set to intersect each other at any given distance, (the point of impact), it means that
the scope and barrel are not parrallel, otherwise the bullet would hit the target high at the same amount as the scope is mounted
above the barrel. Provided the bullet shoots flat for that distance.
Some reloading manuals will state a 'trajectory' for 'X' calibre, at 'X' speed, with a 1 inch scope mount'.
They say that because if the mount were a different hight, the trajectory would be different.
I used to wonder why my rifle, with the same loads as my mates, would always have a higher trajectory than his. Say, 1 1/2" at a hundred yards
for spot on at 225 yds, where his was always less, say 1" high at a hundred for spot on at 225 yds.
I always use high scope mounts on my rifles, I just like the feel and that's the reason.
It is explained properly, by experts, on one of the American Forums, might be Chuck Hawkes, not sure, but it's worth while every shooter
reading it.
I hope I've explained it right, I tend to get tongue/finger tired and can't explain as well as I should.
Feel free to straighten this out, anyone.