Fred:
I hope I'm wrong here, because as a fellow member of the "Rooms that Sucketh" Clan, I'm hoping you're finding some solutions.... but.....
I don't think your panels are reducing that 40Hz hole. My understanding is that any absorbers that would make a difference in bass frequencies would need to be much thicker...and ideally corner-mounted.
Again, I could be wrong...
A question: Was the "before" plot done immediately before adding the panels, and with the mic in exactly the same place, or was it taken from previous tests? Because a mic position just a few inches one way or another over two different testing days might be responsible for that change you see at 40Hz....
