That said, I notice that your image is running wintab 1.4, whereas the latest driver I am offered (from microsoft through the surface book drivers) is 1.3. Could this be causing the trouble?
No, not at all.
ok you have the graph displayed and can you control the changes in it with your stylus ( try to do a linear slope ).
If you can't then do you have a control panel where to setup the pressure for your stylus ?
With Wacom for example add Black Ink as an application and then configure the pressure sensitivity
like in this picture ( sorry in French )