The difference as you are now finding out is that you can't zero if your scope is fouling.
The difference between low mounts & high is that your line of sight will cross the projectile trajectory at slightly more of an angle so there will be fractionally more error if your range finding is out,
but that's utterly irrelevant compared to not being able to zero.
There are no if's, but's or maybe's, if your scope is fouling then it's mounted wrong, you want a good 3-5mm gap between objective & barrel.