Hey my friend.
For HHG it's not a gap filler so we want the fitment to be as good as we can get it. That's why I hammer home here on the OLF that for a bridge if you want to use HHG I want to see a complete contact fit of the entire bridge everywhere with only light finger pressure. If clamps have to force something in place it does not fit.
With say epoxy which is not used much in Lutherie but does have a place it will fill gaps and is more tolerant of a lousy fit.
Other glues are in the middle so to speak but we pretty much always want the best wood-to-wood fit we can get for anything in guitar building.
Some folks are keen to shoot for the least glue line possible and that's certainly a worthy endeavor. When guitars age the finish tends to sink into glue lines that are of any thickness and show and although it's not a structural problem it is visually not great....
Jointing a top is a very good exercise in how well something fits. People "candle" joins meaning hold them up to a window or even a "candle" to see if the light reveals a gap. My friend Link Van Cleave who is a Master Woodworker, had his own woodworking TV show on the West Coast and he was Jim Krenov's apprentice and Link also taught wood working at the Redwoods School of woodworking taught me that our eyes are VERY powerful.
He thought that candling is BS and that with the two sides on the bench in front of us and decent lighting we should be able to see an gap, it appears darker and that's how I do it as a result of Link's advice. So one tool for checking fitment is our eyes and learning to trust them.
I don't know a specific number for any acceptable level of not fitting we have never discussed a tolerance here on the OLF in a specific number sense so that's why you are not getting any answers to your precise question my friend.
Just make the mofo fit is what I do
