@Tom_Hammond check out the series of 3 threads starting here - if what you’re looking for is ‘just’ tweaking overall dimensions, then there may lay the answer… I was also frustrated at first, as I noticed ‘stretching’ in the z axis and slight ‘shrinkage’ in the x and y axes, which I originally thought to solve in the ‘normal’ user interface part. But if you use @ChristopherBarr 's calibration method coupled with @KenCitron 's washing method (see his advice) you will, hopefully, be able to get very dimensionally accurate parts.
Let us know how you get on!
Sol