Finally got some positive results to share
Decided to go with altering the rod lengths, because that seemed to work and I kinda understood how it affects the print when it comes to dimensions. (measured length / desired length * rod length = new rod length ish) basically if the print is too small, shorten the rod, if too big, lengthen it.
these are the measurements I ended up with
in config.g:
M665 L216.750:215.000:210.100 R106.126 H217.714 B105.0 X0.229 Y0.223 Z0.000
M666 X0.601 Y-0.021 Z-0.580 A-0.53 B0.12
after delta calibration, probing 16 points with S4 method;
M665 L216.750:215.000:210.100 R105.838 H217.678 B105.0 X0.229 Y0.223 Z0.000
M666 X0.340 Y-0.123 Z-0.217 A-0.53 B0.12
I printed a hexagon with flat sides perpendicular to the towers. desired width was 75, and the results i got now are X:74,95 Y:74,95 Z:74,85 These could be extrusion issues not related to movement so decided to end here. Printed 30 ish hexagons chasing accuracy...
Decided to print 5 20x20 cubes, one on the middle, and 4 on the extremities of the bed, all spaced 40mm from the center both up and away (40:40) (-40:-40) coordinates and so on. Some measure bang on 20 on one side but 20,30 on the other while the middle one is good on 20,05 ish on all sides. The deviation between the cubes printed on the extremities differ slightly. I think this deviation on the cubes is result of changing rod lengths rather than offsets etc, but currently im fine with these results. Does anyone know how the offsets or tower angles affect the print directly? I know the current rod lenths are not correct real world measurements, and would like to try a more legitimate method of calibrating. Maybe then i could even get accurate parts all over the bed