BOV Opening on Part Throttle when above 4000rpm

[SlowGTS-t]

R32GTS-t, front mount i/c, hybrid turbo of some sort, other bits and pieces.

The BOV seems to open when accelerating past 4000rpm and at part throttle and the car loses power. I thought it was because the factory BOV spring was too soft so fitted an Apexi one. STill does it. Doesnt seem to be a problem at full throttle. Almost as if there is a lot of boost before the throttle which lifts the BOV. Weird

[R31 POWER]

I know it's a stupid Question but is the hose from the plenum joined to the BOV?

I know if it's not theres no presure pushing down on the diafram of the BOV,boost will push it open and hence the leak.