Bed leveling issue/z-offset problems

I’m having an issue with my Mini. The front right and back left corners of the bed are too far from the nozzle, while the front left and back right corners are too close. Now here’s the thing: I’ve gone over this table with a 0.0005” indicator, and the washer-bed distance varies by only about 0.001-0.0015”, which suggests to me that the issue is in one or both of the axes.

So in order to try and compensate for this, I’ve shimmed each washer (between the washer and the bed) and printed a four-corner test to get a feel for how far out the system is. That introduces my next problem: I’ve maxed out the Z-offset at -2.0mm—the program wont let me go further than that. I probably need to hit -2.1mm at least.

So considering that I think the stock offset for me was -1.37mm, that’s at least a 0.6mm dip that my machine is taking over the length of this bed, and now I feel like I’m out of options. Can anyone help me at all with this? Thanks.

Are you raising the bed or are you raising the washer with your shims? Can you upload a picture and point to the shims if they’re not obvious?