Terrain collision detection with another collider - single vertex of heightmap doesn't collide!

Hello! I'm trying to achieve realtime digging with Terrain component. To check, if there is some terrain left to dig I use Mesh collider. But I also tried:

• Box collider (to increase performance)

• Physic.OverlapBox

• OnTriggerStay etc.

Everything works fine, but the collision detection is inaccurate, it does not detect a few vertecies (screenshot 1). My question is: Is there a way to increase the detection of Terrain Collider? I played with some values in Project Settings in Physics, but to be honest I didnt understood many of these options.