Makes sense. I usually put a piece of scotch tape on the side of a case and slide the delrin piece in till it touches. That leaves ~.002" clearance, which has been pretty reliable for me.
These are two pieces of gear that I have found very helpful when it comes to setting swaging depth, that might be of interest to you and others:
Swage "setters": https://www.ammobrass.com/product-pa...s-swage-setter
Primer pocket Go/No-go Gauges: https://ballistictools.com/store/three-gage-pack