Question regarding JRA M21DMR 19.25

I have had this rifle for awhile and either I am very dumb or just do not know what I am doing. With the irons I can't get this rifle to shoot lower than 6 inches high at 100yds with the rear aperture bottomed out. Should a shorter barrel (19.25in) require a taller front sight or should it shoot normally with a standard height front sight? I am almost positive the front on this one is standard height.

Also, it is the M21 model with the integrated scope rail. It is great except I have struggled ever since I put a scope on it with the eye relief. I have thought it was just me but the rail is mounted so far forward on this rifle that I really strain to get a proper view through my scope and it really doesn't matter what scope I put on it. The only way I have found to do it is mount a cantilevered mount backwards which is not correct at all and drives me crazy.

Any thoughts or ideas on this before I decide to sell this thing?