This thread outlines the default settings from a few years back. Your $102 might be wrong.
Grbl default settings - X-Carve - Inventables Community Forum
I would get an accurate scale and determine how much the Z moves for an input jog of " your choice of measurement".
Then you can do the ratio to change it if need be.
How to change the GRBL settings on the V-Carve - Software - Inventables Community Forum