I'm learning some Michael Hedges pieces by ear... Woman of the World, Two Days Old, Ragamuffin etc.

and I've known about slapped harmonics through videos of guys like Andy McKee and Antoine Dufour on youtube, as well as performances by Hedges himself. However I've never been able to get it to ring out 1)consistently and/or 2) loudly. I've heard it's not how hard you hit the guitar at all (I'm not senselessly hitting the thing), but how quickly and cleanly you touch the spot where the harmonics ring. Is there any way to teach this, tips, advice, etc.? I'm a perfectionist and want to be able to do this well
Fender American Strat --> Vox Crybaby --> Keeley Rat --> Marshall AVT 100
I assume your doing slap harmonics on the 12th fret? If so, you gotta hit them clean like you said. Hit them right on the bar between 12 and 13. Just keep practicing.
which finger does one usually use? it seems with my ring finger I can produce the harmonics easier but they lack the volume, and with my middle/index fingers they produce certain harmonics very well but not with much precision
Fender American Strat --> Vox Crybaby --> Keeley Rat --> Marshall AVT 100
use your middle finger, and put all of your other fingers "on top" of that finger... it's all in the wrist you know, don't wave with your hole arm.