Yep that is the issue. I do not know of any stock style PCV that will transition below 10 in, Mopar, GM or otherwise. The Wagner part can be made to operate in dual mode at your vacuum levels. See here:
http://mewagner.com/wp-content/uploads/2017/10/DF-17-Shop-Manual-R7.pdf
Now, one thing.... your carb setup can have a lot to do with the idle vacuum level. Especially the secondary throttle stop and the base ignition timing can have a lot of effect. We went up 2" with proper setting of the secondary stop screw, and associated re-tuning. That is the 1st thing to do...but you'd have to simulate a PVC at low flow to get there.
