I think there is a small error in the formula to compute the space between nodes when using the internal extrusion with the keyword "Extruded Mesh Ratio".
By definition in the documentation, Extruded Mesh Ratio is the ratio between the first and the last element and the element size is assumed to follow a geometric progression.
I made a test with
Extruded Mesh Levels = Integer 11
Extruded Mesh Ratio = Real 4.0
which do correspond to 10 layers and I expect that h_1 / h_10 = 4
The different h_i are
which is a geometric progression of common ration r = 1.1487
The ratio h_10/h_1 is 3.48 (which is r^(n-1)) where I would expect it to be 4 (and 4 = r^n)
Solution is in MeshUtils.F90 at lines 9816 and 9820 where 1.0_dp/n should be modified by 1.0_dp/(n-1)