I tried a ping-pong ball with 4 circumferential ports and a pitot/static probe in various locations. None were any better than this vertical tube. On my racing quad, I'm finding that a static port directly on the pixracer case performs well for ALTCTL; and that the altitude readings from a small GPS module are useless.
yes, I've been flying with a non-3DR external mag/gps, and I can change rc.sensors to make any of external, 9250 or 5883 the primary mag. (with recalibration required each time you change it, unfortunately)
well we got it to work on stable. switching back to master everything worked. after re-calibrating with master it complained about too big offsets on the internal mag. after a reboot it was happy though