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Ok, I've worked on getting my axis calibrated, but when I have Z=0 in the center and move out to one of the towers (any one) it's off by 0.2mm (closer to the tower is 0.2mm lower than in the center).

Any ideas what might cause this? I'm guessing maybe my towers aren't perfectly straight??

If you have verified your build surface is flat then you have to adjust delta radius. How to adjust it is based on your firmware. There are a couple of topics about delta radius.

Remember delta radius is used to adjust for the conical travel of a delta based printer not to compensate for a build surface that is not flat.