If I bank hard so that the thrust is increased a lot (via the built in bank angle throttle compensation of AV/AH), the throttle gets stuck wide open and it climbs way up high after leveling out. This makes sense because the props are apparently making a high pressure area around the FC and because of the high pressure, the FC thinks it's altitude is too low, and the AV/AH adds a lot of thrust to compensate.
I have what I believe is a standard amount of open cell foam (4-5mm?) on top of the baro. It's lightly compressed to about 75% of original thickness. My quads are 330-500 and run ~1000KV motors on 3S. They have fairly large props; 9-10 inch, so the prop blast does come inboard on the arm a good ways.
My issue is that I can't imagine that adding more or thicker foam would fix it. The high pressure would still seep in, just slower and it would take a longer time at high throttle for the undesired climb to start, but it would still start, and adding that much foam would effectively delay the baro sensor and cause vertical oscillation. I've had that "vertical oscillation caused by too much foam" issue before too.
On one quad that effectively has the FC between two body plates, I have managed to reduce the issue by closing off the side gap between the plates all the way around. I am guessing that reduces the prop blast that gets to the FC and reduces the over pressure.
I have considered reducing CruiseControl MaxThrust (which is used by AH/AV) to just below the value where this can happen, but that would be a last resort because it decreases the fun factor of the instant braking that you get from the AV/AH's built in CruiseControl when you pitch back 90 degrees in fast forward flight.
Is the solution that I must find the proper way to seal the FC here and vent it there on each different quad design, maybe add multiply vented chimneys where needed?