What a single point does well is to "correct" enlarger exposure for changes in camera exposure (purposeful or inadvertent). This is possible because most negative films have some latitude. This may be why you see little difference between prints from differing EI's with PanF and Delta 100.
(Side note. As reference points I use; my palm, my camera bag, my truck provides both black and white points, asphalt, northern sky, grass, in studio setups I use a rag doll ... Any "known" reference point can work.)