If you are bleeding air off you should just keep making more boost as the turbo is pushing more air into a sort of closed system or brick wall and the wastegate is closed.
Nah, I don't buy that mate, although I appreciate your logic. Bear in mind that this bugger is so restrictive that you can actually feel it choking once you get to around 10 psi. The boost is not read from the turbo but from the manifold.
If the exhaust is so restrictive that it actually flows at low boost levels but increased boost levels severely affect flow. A turbo will simply not 'spool' or boost when what you have said above occurs.