If you're talking about the top pic rail that's on an AR receiver, and used alot on the handguard rail, there shold be plenty of room on the top of the receiver.
The only issue that might occur is if the rear BUIS (if you're using one) is too tall/bulky so it interfers with the 3X magnifer, that behind the Sparc.
Then you would need a lower-profile rear BUIS to allow the 3X magnifer to overhang the rear BUIS.