[350HP930]

You are missing the fact that the pressure that cracks open the wastegate and the pressure that opens it a few millimeters can differ by a few PSI.

As the turbo reaches its sweet spot the wastegate often has to open several millimeters and that requires more than the base opening pressure of the wastegate.

For that reason everything from the flow dymics of the compressor and turbine to the wastegate spring rate and valve and diaphram geometry cause a complex control equation that causes the kinds of issues this thread is asking about.

its also the reason why 930s with functional wastegates will make more boost on cold days than hot ones.