Joy sent me the following
"The indulgence V2 has tight airflow with 510 and 40X adapter, it is not as easy as the Riva and 510 or ego, but it dose work."
I was having the same issues. I just enlarged the vent holes on the side and it now allows for an easier airflow.
By the way using a copper spring did greatly increase the TH and now gives a fuller vape.
Each of these hints will improve the unit, I too and working with V2 and now I am enjoying it better than I have since day one.