Surface auto disable

[OctaviaMelody]

Hello! I'm currently exploring surface mode and have a question about how it works. I tested it on a 7" drone with an MTF-01 sensor, and now I've switched to a Benewake TF02-Pro lidar. I also changed the maximum values ​​for inav_max_surface_altitude and nav_max_terrain_follow_alt to 2000 (20 meters) in the firmware. Now I'm running into a problem: at a certain point, my drone takes off at high speed, as if disabling both Alt-Hold and Surface modes. When I return the maximum value to 1000, everything works reliably. What could be causing this? My best guess is that the lidar could be tilted too far, causing it to lose signal. I specifically configured the Benewake TF02-Pro to indicate it's at 10 meters when the signal is lost, so I could check. But even in this case, when I tested the drone, it simply disabled the modes and flew 30 meters away. Please tell me when exactly it disables the modes and how can I modify the drone to achieve stable flight at an altitude of 15-20 meters.

[sensei-hacker]

Benewake lists the performance as 0.1 ~ 40 m @ 90% reflectivity.

90% is somewhat better than a whiteboard.
40 meters is the best you'll ever get in a darkened room if it's pointed at extremely reflective, bright white surface.

If it's pointed at a white tile or concrete floor in that same darkened room, figure 20-30 meters at best.

If it's out in the sun over white concrete, 10 meters.

Over dark grass or soil, 5 meters.

how can I modify the drone to achieve stable flight at an altitude of 15-20 meters.

A radar altimeter. ~ $5,000

The good news - if you're 15 meters above the ground, you probably don't need to be diving into every ditch and bumping up for every speed bump 15 meters below. You don't need surface mode when you're not at the surface.