Marlin Z adjustment

I'm running a Sovol SV01 on Marlin 2 bugfix with 9 point manual bed leveling. I'll admit up front that I don't know the mechanical details of my Z axis but when tuning (Bed Z:) I can see the a difference in the print by changing Bed Z by as little as 0.005.

The bed is a glass sheet which is pretty flat, using the Level Corners option the center is nearly always correct.

The step size (MESH_EDIT_Z_STEP) for manual bed levelling defaults to 0.025. Given such large steps I can't see how the results are as good as I'm getting.

I don't really have a question, except I feel like I'm missing a decimal point or something.

According to my last attempt at manual bed leveling I have a range of 0.1 which just feels mad.

Recv: X:0.00 Y:0.00 Z:0.03 E:0.00 Count X:0 Y:0 Z:0
Recv: ok
Send: G29 T
Recv: Mesh Bed Leveling ON
Recv: 3x3 mesh. Z offset: -0.02500
Recv: Measured points:
Recv: 0 1 2
Recv: 0 +0.00000 +0.07500 +0.00000
Recv: 1 -0.05000 +0.02500 -0.05000
Recv: 2 -0.02500 +0.02500 -0.02500

Maybe just the +0.075 is spurious but the print is working so well across the whole bed I'm loath to bugger with it.