My other car is a MINI!!!!
will almost certainly be a split pipe or boost leak somewhere.
From the figure 20psi, I'll assume it's an AUM and not an AGU? I'd be looking at all the PCV pipes under the inlet manifold, a small hidden split in these lost me 5psi of boost for a very long time that took me ages to find a few years back. As Bill said I'd also fit a yellow spring in the DV, and check over all the charge pipes and connections. AUM's have a nasty press fit type clip down the back of the engine bay which famously gets tired over time with the movement of the engine and allows a boost leak.