Same here. The biggest trick is to frequentmy move the heat gun away and put my hand on the playfield. If it is too hot to put my hand down, the heat gun is too close/set too hot. Patience is the key. And you must avoid pulling off the mylar too fast, and only pull up where the glue has softened. Easy peasy.
I used the same technique earlier this year to pull up my old vinyl kitchen floor with a heat gun.