Down Radar Questions

FC: Cube Orange (4.4.3)
Radar: CUAV ISTRA24

My goal is to accurately maintain the distance from the trees when flying automatically over trees in the mountains (spraying pesticides for pests).
I followed the settings as described in the manual, but it does not work properly. When measuring a tree, its altitude increases.
If the aircraft altitude is 20m and the radar max value is 20m and you go up a 10m tree, isn’t it correct that you should rise 10m?
If you climb up a tree, you only go up 2 to 4 meters. And when you pass the trees and come down to the plains again
It comes down further than the existing 20m (2~6m) or remains at the same altitude it ascended from.
Can you tell me what the solution to this is?
//Radar is measuring trees properly.

i think you are using surface tracking function instead terrain following