Excellent point, forgot about that myself.. but both of my 308s wear JP round tubes with no rail mating up to the upper. The add-on rails can be either cowitnessed or raised to match the profile on the taller upper. I actually run a std on top of my tactical build to add a buis, but with the AR332, I don't have room for a rear sight. I am awaiting my Strike Eagle and then I may likely add front and rear flips. I run a tall rail section on the underside in front for a bipod to attach.
Pics of the tactical build.. (sorry, pupper kinda photobombed that one.... lol)