The height above the barrel doesn't have any influence on your problem
and the RR cantilever is co-witness. ARs just about need that height for
proper/comfortable cheek weld.
If it shoots the same amount low at 50 yds and 100 yds, then...
Did the impact actually change when you adjusted elevation?
Are both mount cross bolts bottomed in the rail slots?
Is mount flush to top of rail at front and rear?
Is the mount attached to rail on receiver only and not
to rail on handguard also?
Have you tried moving the whole shebang forward/backward one or more slots?
Is there clearance between ring and turret housing?
Did the scope lay flat/level/straight/not canted in the rings before caps put on?
Have you tried that scope and/or mount on another rifle/upper?
Do you have iron sights or another scope you could try on that upper?
The 2 bolts which attach the RR mount to your rail have to be bottomed
out before torque- down is really effective. The thru- bolts are pressed
into the mount and ultimately bottom against a shoulder, making them
solid. If the bolts were merely pressed in and not bottomed at the
factory (it could happen) then there can be a false tight spot and mount
Look at the little round bolt heads and make sure that both are sunken below flush 1/32".
RRA mounts are heavy tactical and quite capable of crushing/distorting
your tube if over torqued- wouldn't use more than 15 inch-lbs. on the
If it turns out to be the mount (doubtful- they're tanks), then RRA customer service will make it good- their cs is as good as it gets.
In this pic you can see how the mount is flush with rail and see the cross bolt 1/32" detent. Note, this is not the cantilever mt: