I'm not one to agree that there is a 'bubble' of high pressure under the rotor system in a hover, although we may all be guilty of describing it this way for simplicity. I do notice when pulling pitch during takeoff, the VSI indicates about a 150-200 fpm descent, as well as the altimeter will drop about 40 feet.
Does anyone else notice this, or can anyone explain....or am I just being silly?