ometimes the edge of the chin flap on a trifold can seem to hang free even on a mask that passes the fit test - if another part of that flap has created a seal. The chin flap edge does not need to seal if there is a seal elsewhere.

I have this problem with most masks so if thats the case then I guess I'll pass. Now I'm looking at Benehal mask - https://www.amazon.com/Approved-Particulate-Respirators-Individually-Wrapped/dp/B09WVD7GVQ have you tried this one?