Hi and welcome!
I think this was meant to read "The boost controller will only increase, not decrease boost".
Like terribleturner said, you just need a restrictor plate.
Most of us over here like to restrict the boost on our JDM TT's to 1.2 bar, when you fit a bigger bore exhaust and remove the catalysts then the boost will increase substantially. There isn't normally any need for a boost controller as it will only increase boost.
The best place to fit the restrictor plate is after the decat pipes(down pipes) as this will keep the build up of heat away from the turbo's .
When I fitted the restrictor plate it did keep it down to 1.2 bar, recently it's been going to 1.3 bar. I really need to fit another one with a smaller aperture, it's a bit trial and error really!
I'm surprised you're not hitting fuel cut though.
You also need to make sure you've got some decent spark plugs fitted or it could start misfiring.
Denso IK24's are good but not cheap!
NGK BKR7E(6097) are much cheaper but need to be changed more often, over here they're about 1/5 the price of the Denso.
It must get pretty hot over there at times, also worth making sure that your interccoler is in good shape.
I'm sure others will tell you more!