I would not like to display with QNH set - keep it simple! An airfield elevation of 2996 ft - lets call it 3000. If you need 2500 ft agl over the top, you should see 5500 ft on the altimeter. 1670 ft agl sounds like 4500 ft indicated plus a small amount of spare. As I recall, the F-16 has a strip altitude display in the HUD. Any experienced F-16 drivers like to comment on the potential for misreading HUD altitude when in a high pitch rate manoeuvre such as this (reverse half cuban)? What block aircraft are the Thunderbirds using and therefore what is the HUD symbology?