The axes of these maps are nmot (engine speed) and vpssplg_w (requested pressure ratio) and the Z-values are pressure ratio across the throttle body. Look for the values in the table that start to exceed the threshold of PSPVDKUG (generally 0.95) and approach 1.0, and trace up to the vpssplg_w axis. The pressure ratio minus 1 bar at this column (when stock) should be your wastegate pressure (3-6psi for stock wastegates).

An easy way to make an initial pass is by only modifying the vpssplg_w axis data. Take the ratio of the new pressure to the stock wastegate pressure (e.g. 1.8/1.3 = 1.38), and correct the vpssplg_w axis by multiplying each value by this ratio. This roughly sets base boost for proper throttle control. You can further tune this table by making sure areas below the spring/cracking pressure of the wastegates stays below the value in PSPVDKUG.

The pressure axis is a ratio of desired manifold pressure : ambient pressure.

vpsspls_w is a desired pressure ratio pre-throttle pressure : manifold pressure.

vpsspls_w is used to convert desired manifold pressure pssol_w to desired boost pressure plsol_w.

It is also used to regulate pressure pre and post throttle via the throttle plate. If vpsspls_w is > 0.95, then the throttle plate is forced to open that percentage towards WOT. Anytime  vpsspls_w is 1, then the throttle is forced to open 100%.

It has no other function and no direct influence on the boost PID controller.