That's likely due to the factory calibration of how much air it's supposed to draw in from the IAC and how much from the PCVs through the intake tube/manifold ports. I doubt at anything when the TB is open - and the IAC is shut. I imagine when you let off the gas at high RPM it's even worse than idle.
I'd rather adjust the idle a bit than have oil in my engine - just personal preference.
The whole issue of metered vs unmetered air is bunk; the PCV is basically pressure from 2 factors - one created by blow by and one created by simple heating of components and oil. heat stuff, it expands, heat it in a closed environment, pressure grows. Blow by is indeed air that was metered, but it already went through the combustion chamber, if you reintroduce it, it's new, it's much like hooking up your exhaust to your air filter - except it didn't escape through the exhaust valve but next to the piston. Either way, it's new air. The heat generated pressure is so small and gradual when the engine warms up that it doesn't really affect anything. The only reason you're seeing a large difference with breathers is because the engine is calibrated to use the IAC for a certain amount of air and the rest from the pcv.
To each their own
My solution, for having a paxton on the car - I didn't like their one way valve deal - so I'm going for a vented catch can. Kinda like a breather but should cut down the mess almost completely. It's gonna be mounted in the empty space by the brake booster, once I get the right hose barbs and whatnot...
