Has anybody removed slapped felt headliner right against the roof?

That does work well.

Also, using a sound deadener against the metal with strong spray adhesive does more for reducing resination than attaching it to the headliner, If you do both and hit the insulation with spray adhesive on both sides, it also helps hold the card liner up and helps prevent sagging. I use a thin sound/ heat insulating sheet that is made for doing just that. It has a reflective surface on one side and helps regulate temp inside to out.