12 years ago, the magnetometer was under the vertical stabilizer. That worked great. Then the upgrade. The new unit now included the magnetometer and ADAHRS together. Under the Vert. stabilizer, it was overly sensitive in pitch.
I moved it directly behind the baggage bulkhead. That worked great till I went to Oshkosh and packed the baggage compartment full with the tow bar on top.
Next, I used the Van’s mount with current results. Today, moved it down to the longeron level, directly below the Van’s mount. Same results. My guess is the seatbelt cables are throwing it off now.