Yeah, you're correct. But add to that at least 1mm for the wire that has to be soldered on and you're left with 0.5mm clearance for it to move down which doesn't sound like it's enough. I don't know how RainZG did it but I'll be receiving one soon so let's just see if it fits. If I can't fit it in then I just use the 22mm washer and mount it on top of the unit like described in this topic.
I soldered wire horizontal and also sanded about 1mm from body, so body length is now ~6,5mm instead of 7,5mm
also sanded 0,5mm from positive pin. With that everything works and my atty's still sit flush
EDIT: You could also play a bit with positive pin on flask so you don't need to sand 510 body