tracking changes in z height of material.

I am engraving 2' x 2' plaques where the metal is close, but not exactly flat. And any change in depth results in less than stellar final products, because the text i am working with it pretty thin. I have a dual drum sander that get things closer to flat, but only closer. I am currently using a spring loaded tool, which does make things a little better, but my depths across multiple pieces are inconsistent. Sometimes it is a heavier cut, and when the pieces are lined up the depth changes become very apparent.
I have a Laguna IQ Pro.
Is there any machine, or add-on that can track the changes in z height so that my letters are consistent?
Any other ideas?

Check out Autoleveller, that's what I have been using for that purpose.