I have never gotten it to work by pulling hot plastic over a plug, It is pushing the plug down through the hot plastic that works. When crash molding parts out of white plasticard, like cowls or spinners, 20 thou card works and is very thin when finished. So you need a source of fairly thick clear sheet. Check Evergreen
https://evergreenscalemodels.com/col...e-clear-sheets
I always support the heated plastic/cut out plates sandwich over a bowl or coffee cup so I can jam the plug down firmly. You have to be quick and not hesitate. Heat it, hair dryer is an excellent idea, slap it on the support and stick the plug down firmly in one smooth motion. You will mess up some, but you will get a usable piece as well. OH yeah, Slightly bevel the edges of the cut out in bottom plate, it helps the hot plastic stretch as you push the plug down
sp