I suppose the first answer is "maybe you shouldn't be trying"... but I am

I have a V40 2.0T (the one with the 12T turbo), and have had an MBC forcing 12psi for the last year. Recently set up an AFR gauge and thought to push it further, but no matter what I do it won't go above 12psi.

The MBC is screwed fully in now, and it's still 12psi.

I'm not exactly at my wits end, but it is annoying (I wouldn't have spent money on getting the AFR gauge set up if it wasn't possible!). Current suspects in my mind would be the recirc valve and/or the wastegate ... but the wastegate is surely controlled by the MBC?

There doesn't seem to be a boost leak as such, it just won't boost higher than 12. How do I check the recirc valve/wastegate operation, or am I barking up the wrong tree?

Thanks, as always, in advance.