The Z moves the way it does because I don’t optimize Z moves yet for DSP systems (the feature is still in test for GCode systems, and DSPs are next).
The test itself is simple - it draws a bunch of lines at varying Z heights so you can tell where the optimal focus point is (the thinnest line).
For the range, I suggest using your normal focus method as a starting point, then using the “Get Positions” button on the Move window to figure out the Z height that gives you, then make a focus test of Z-5 to Z+5 or Z-10 to Z+10 (for example) to figure out if your existing focus height is ideal or not.