I agree with most of that, Nissan would have put the hole there for driveability, it stops any surging of the vehicle when backing off, the car used to surge and drive funny when backing off after a squirt, also make noises from the bov as it opened only a small amount. It is tune related as it doesn't do it anymore with the stock turbo running 17psi, or with the last tune I had on the old turbo.
The next option is to place a grub screw in the hole and drill it out say half a mm at a time and see what happens. I think a smaller hole, say 2mm, would work well. Or just a larger compressor wheel.
You will need a retune for anything you change now Ironpaw. At this level any changes can melt holes in your pistons pretty quickly. If you can get the wideband in and log a few squirts, email it, Cihan can probably tell you if you need a re-tune.