I don't know if there was much real technical basics for what I posted about coil covers. I know some of the information was true of the old TR detectors about hot spots and discrimination. I recall a couple of manufactures that actually had about a half inch air gap between the coil and coil cover bottom thinking if we scrubbed the coil then there would always be that constant height.
My personal opinion was my last statement in that I just figure it is better to wear a coil cover instead of the coil. For the most part I see a coil cover as just another way to tack on a few bucks like how many coils can we figure out how to use. It just goes with the hobby to have a detector, then more coils, then headphones, probes, etc. You would think with a $1,500 detector we could take it to the park and drop it off then go get it in the evening with all the coins it found for us. Ha