Actually the dams/pods/lids etc did not affect the HOVER performance at all. If anything they REDUCED it because of the extra weight. What they did affect was the vertical LANDING and TAKEOFF performance. As stated above, interaction between the airframe and the vertical jet eflux and recirculation of hot air into the intake was what was managed by all the bits and bobs.
The hover was always carried out in "free air" outside the effects of recirculation, airframe impingement etc. It was possible to hover at a weight that would "spike" the engine if you attempted a VL.
Swing the Lamp!
Mog