AFR misleading? Plugs tell a better story?

The short answer is;
Reason #1; my experience;
Every time I have run the PCV to the secondary side,on a dual plane street engine, that requires idle bypass air,and does not have a 4-corner idle; ( about 99% of my tunes,lol, I get idle-tuning grief, which is right away much reduced or gone when I reroute that hose to the primary side.
Interesting. That is exactly the setup I have... except that I drilled all four plates 3/32" so I could set the primary and secondary transfer slots both "square".
Just wondering what kind of grief you are having?