As for fixed, throw the chain on roughly, spin cranks for a bit to knock off the excess wax and then do the tension properly.
I do this. Maybe I don’t do it enough. I still find the chain stretches a lot. I guess that’s wax on the interfacing parts wearing/compressing or something.
Also.
Don’t wax your track/ss chain quick links.
( or even better … don’t use quick links )