Bill Tindall, E.Tn.
What works for me is to spray in good light and look for a full wet coat, but not so wet as to get a run. If with the first pass I don't see full wet coverage I adjust some of the above variables to achieve a full wet coverage. If I see a thin area I will spray over it to get sufficient coverage. I'll diddle with the dilution solvent to slow evaporation if the wet coat is drying too fast to level or allow a quick second pass to add coverage.

Clearly one time measuring a partially evaporated film thickness on a test piece will provide no guidance for spraying my furniture. What I will do is spray some test surface to get a feel for feed rate. The test surface could be a saw horse leg, or piece of cardboard.

It is not rocket science. My daughter and granddaughter spray easy to spray pieces successfully, fist time. I tell them to spray a wet coat, they do, and success.