High profile rings or extra high profile rings are prevalent on most bullpups, for the previously stated reasons. 1st and 2nd Zero can be set, especially with utilization of elevation adjustable rings, to work quite nicely from 15 yards to 150 yards. With most guns and calibers, you will be required to learn your hold under (up to 1/2 mildot for ranges inside a 50 yard 2nd zero) but this typically translates into less than 1/2" differential in POI. Negligible in my opinion. Targets inside 15 yards are rare but would require a hold over up to the distance between centerline site and bore @ point blank. The main detrimental factor is, controlling cant as this is amplified by the higher site centerline relative to the centerline of the bore. As an example, for my Edgun .25 w/ 2 5/8" centerline differential, a 15 degree cant will translate into just under a 2" POI shift @ 100 yards. IMHO, a scope level is mandatory for most bullpup configurations. The other big factor is, generally bullpups are poop for left handers, with the exclusion of the Vulcan, which has been designed to accommodate this eventuality utilizing a reversible bolt and flush mount magazine.