After struggling with the Surface Level and having inconsistencies with it, I think one thing it could really benefit from is a value input box alongside the slider, like how attach point offset/rotation fields have.
This will allow you to:
a) see the current surface level value
b) type a voxel level manually/use mouse wheel to make minor adjustments
As it is, it can be quite fiddly to just move it up/down in small steps, often wanting to jump up by a couple.
Just the natue of grabbing and moving with the mouse.
Some finer adjustments would really be helpful I feel.
Concept Image: