Man I use to have the same problem. Please, please, please keep an open mind because I am not trying to offend in any way.
Yes, I believe you are over feeding. I know I know....you've vaped for a long time and you feel like if there was a learning curve, you'd be past it, but the fact is that some attys are just freaking tough to use regardless of how long you've been sportin' a bottomfeeder! I'd be willing to bet you are using a 510 atty and the reason I say this is because 510's are by and large the most finicky to use. Trust me! I've had countless mouthfuls of
juice just like you and even after I have found the sweet spot for an atty, I still sometimes overfeed! With some attys, if you squeeze the bottle until you see juice at the battery connection, you've over fed. Yeah, I'm serious. With some finicky attys, even a blind squonk may be too much unless you are extra careful. Heck, try using a HH357.....unless everything is just perfect (amount of juice in atty, drawing at exactly the right speed, drawing the exact amount of time) you are gonna end up with a tongue coated in juice.
Now, there are a few ways you can fix the problem. The first one you already discovered. If you create a choke point in the air flow between your mouth and the heating element, it will greatly reduce the amount of juice that ends up in your mouth. The vapemate creates such a choke point....so does an empty cartridge....so does that pyrex drip tip that was recommended earlier. Using a choke point will greatly increase the margin of error, but it will not completely eliminate the problem.
The second is to draw slower...but that is going to end up frustrating you because you've already discovered the perfect draw speed for the atty to get the thickest vapor possible out of that atty and who wants less vapor?!?
The third way is to feed less. I already stated that feeding to the point where you see juice in the battery connection is too much for some attys....give it another go feeding it even less (again, I am not trying to offend). You may surprise yourself, even if you've been
vaping 5 years with the same atty and mod.
The fourth is to change the atty you are using. Each and every atty has a list of advantages and disadvantages and one of the things that I use to judge an atty is the margin of error on over/under feeding. 306 attys are more forgiving but not all 306 attys are created equal. The two most forgiving attys I've ever found (and they happen to be 2 of my 3 favorites) are cisco spec 306 (from avidvapor....get the one with the bridge intact for an extra little boost in the margin of error) and the io6 from IKV (this atty is almost impossible to flood to the point of juice in your mouth). 901s are also more forgiving than 510s but their airier draw isn't a favorite of most people. I'm glad the option is out there for the people who love 'em, but I ain't one of em.
I hope this helps and I hope I didn't offend. Keep working at it and I'm sure you'll be able to turn all the juice in your atty into vapor instead of mouth wash. Good luck!