First, no matter how many "experts" say it is OK, I have always been of the opinion that stretching plastic fly lines to reduce coils is NOT a good idea and accelerates the cracking process, especially if the line is cold. I have done SOME stretching to a stubborn coil or two, but I'm talking about a foot of line, not 50 -60 feet.
Let me add that I have plastic fly lines in rotation that are 20 years old so maybe I'm on to something...
😉
A couple of things I noticed with fly lines over the years...
Harder, less supple lines coil more. Some folks prefer a hard line because they say it works better for them, but I avoid them like the plague. FWIW - I fish real silk lines too which are more supple than anything and they cast & shoot like a dream.
In my experience, better lines coil less. For that reason I don't cheap out on fly lines, I take care of them and clean them regularly. My preference for all of my trout rods is the SciAngler Mastery DT.
DT's don't experience the severe coiling issues you can have with the running line on WF lines. For that (and other reasons), I fish DT lines which are really all you need on a small stout stream.
ALL plastic fly lines need time to break-in and achieve maximum suppleness which reduces coiling. It is no coincidence my older lines are the lines that are super supple and never coil.
Good luck!