Ok, just some pics and a little about on this.
I tapped and loctited a 6x5mm grub in the reference hole:
I then drilled a 1.5mm hole above that so it references atmosphere now instead:
You can see it along the tube below the hat. This is the better place rather than that moulded bit as it better protects the hole from water ingress.
Ok what this now does is gets rid of the spring limit for higher psi operations, virtually unlimited holding capacity now. But flip side is that it can introduce surge. Not recommended if you are running standard boost. But a quick guide here if you want after market characteristics with oem quality and not spend $300+ for a leaky aftermarket bpv.
This is soft material. Tap is very easy, and the hole drills very easily too. Be careful, and make sure to clean it out of shavings good. No top hat crushing required to preload the spring.