We could use an MEF database (see https://www.faa.gov/air_traffic/flig...ts/aero_guide/
The Maximum Elevation Figure (MEF) represents the highest elevation within a quadrant, including terrain and other vertical obstacles (towers, trees, etc.). A quadrant on Sectionals is the area bounded by ticked lines dividing each 30 minutes of latitude and each 30 minutes of longitude. MEF figures are rounded up to the nearest 100' value and the last two digits of the number are not shown.
Not super accurate but it would be a relatively small dataset and it should actually make the tracker operate properly in mountainous areas.
Another idea is with an onboard receiver like your new MTT4B we could listen to the aprs band. If we hear more people transmitting we're probably up high and we should use less power.