what gun have the lowest height over bore?

i like precision, being able to headshoting an enemy with my AR is satisfying for me, but sometimes when im trying to aim at 20meter the bullet shot lower than my optics crosshairs. i understand that there’s some realistic aspect to it, but doing the zeroing (page up, page down) can’t go lower than 30meter (im using g45 magnifiers and eotech). i find that MK18 (or m4a1 with short barrel) has the lowest HOB with my current optics set, while gun like m16a1 (and any gun that have upper carry handle) shot even lower.