So I am putting a flat top upper on my rifle that used to be in a traditional A2 configuration, but I want to scope it. There currently is a standard A2 FSB on there. I know the F marked ones are a bit taller to accommodate sights mounted on the flats Is this assuming an A2 handle/sight or any sight??? In looking at the options, I see that the bolt on carry handle sights clearly need the higher FSB, however, the Magpul buis arent that tall... can I use them in conjunction with the standard height FSB???? ANyone know?