From my understanding it shoulden't really matter, its dependent on your situation on how you want it mounted. Either way the device should perform fine. If you do want to place it on a desk horizontally, the vertical base portion should come off and you would be able to place it flat on a desk. The rubber feet can also come in handy if you were to mount the device on a wall.
It is all based on what works best for you. Performance should not be affected based on they position you choose.