why the value changes

The wheelchair is running on a flat road.
Obstacles with steps appear during driving.

I want to take the acceleration value obtained by that impact.

But why does the value change just by slightly changing the distance from the obstacle?

For example, when the distance to an obstacle is 1000 [mm], I changed 1 [mm] or 2 [mm].

Is it a mesh problem? The mesh level is set to 5 when importing.