My actuator is an adjustable, set at 15psi with the split dump it wouldn't hold 15psi to save it's life (same for stock actuator and RB20 actuator...to be expected) adding more pre-load was just seeing a bigger psi peak which still dropped off to 11psi.
With the bellmouth fitted, when pre-loaded to 15psi it holds, yey!
Moral of the story, with the turbo on my car the split dump didn't seem to be beneficial at all and led to boost drop-off...I suspect low pressure on the wastegate was helping it get pulled open by the exhaust gas up against it.