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I am going to do my best to explain this. I am trying to get my bed level and have been messing with the horizontal radius also. What happens is that on the X axis going left and right from center, it is fine, but on the Y axis going forwards and backwards, the nozzle comes up. I am not sure what else to adjust to fix this. Any ideas? I attached a diagram to explain better (areas approximate).

How much? +/- 0.1mm or a lot more of difference?
In the meantime, I would check the screws that hold the onyx to see if some of them are more tight than the others.