Not sure if this is stupid or not, but I use a corner of my metal scraper to lightly scrape the surfaces of the gouge, then swab JUST the gouge with some 100% isopropyl alcohol briefly, and dry (to prevent spreading into the surrounding base area).
Then I drip a ptex candle into the gouge-- making sure to burn only blue flames, no yellow/orange.
Then I wait a few minutes (not hours) and scrape.
Then I wax.
My repairs don't fall out. Though some of the repairs in certain shaped gouges (mainly those that are very narrow but deeper, and perhaps at an angle) have cracked a bit visually, but remain solid... and take up plenty of wax!
I can't say what the measurement is, but I avoid filing really shallow gouges of any length-- those that, subjectively, seem more like structure than "gouges." I base that on feel and visual inspection, figuring if it's too shallow, the repair won't hold since there's basically no material to grip on the sides of the repair.
At the end of the season I'll get a grind/structure on the bases, and I won't do that again until the end of the following season.