Bracket, you can access the internal spring which sets the sensitivity.For example, by using a very light spring (ie, one that provides just enough force to return the diaphragm to its un-triggered position when the. Pressure is removed), it's possible to get a switch to trigger at just 5cm of water (~0.5kPa or 0.08psi). The external adjustment would then typically give a range of about 5cm to 7.5cm of water, but of course, this will vary depending on the unit and the spring used. Put in a stiffer spring and the adjustment.
Another issue is that any wiring diagram or schematic is subject to copyright so no one should be publishing them on the Internet anyway. As far as I know there are no official repair manuals and schematics for UK washing machines and other appliances readily available.