I'm using an Aerotank but......I always put a 510 to 510 shorty connector in all my mods so I don't mess up the threads

No probs with mine
an adapter like
this one?
Just like the short one on the left in that pic
Perhaps you should consider instead this one:
Tank Airflow Controller
I've got the 19 mm in diameter, it overhangs just a little, but has better looks and can protect the threads and control the airflow.... well, at least that was the second intended purpose. With some atty's it works in that way, with others doesn't.
With eGo threaded atty's you'll still need an 510-eGo adaptor, and this ruins the AFC function... As a matter of fact, I had to open wider bores for my mini Protanks 3 (up to 1 mm), discovering in the process some brass where I did expect stainless steel....
Nobody's perfect.....
Here you have some pictures with some of my daily running atomizers....
Did you say something about a KFL too big?.....
The last one is a Fogger v3, 23 mm diameter, so you can figure out how much would it sing if you dare to top your iStick with that big RBA that you're hefting....
I can tell you the Fogger turns our iStick in a heavy nosed thing, but it is still bearable, because you can put your finger on the protuding overhang to get a really goog grip of everything (an it serves as defensive weapon....

)
I use a '100 Pipers' whiskey flask pouch as friendly bag for the iStick and its atomizers.... Funny to see how people gets embarrashed when I lift up my "booze" pouch.....but not to drink.....