@polbofree I'd hope you gould get a bit better than that, but I don't have a smart effector so can't say for sure. I would say that such variations could also impact how accurate your delta calibration is so I would definitely look at improving it. A couple of things to think about/check:
Are you probing with a hot nozzle? When I used a nozzle contact piezo I always heated to 130deg C and did a double probe (i.e. two G30's). That was hot enough that any filament on the nozzle got squished after the first probe, but if I went much hotter, the nozzle would damage my bed surface (I use a Ziflex flex plate).
Have you gone through the smart effector comissioning wiki page (particularrly the section on settingb the sensitivity)? https://duet3d.dozuki.com/Wiki/Smart_effector_and_carriage_adapters_for_delta_printer#Section_Commissioning
Your M558 in config uses probe type P5, but I beleive P8 is recommended (it's the same but unfiltered for a faster response)
In general, nozzle contact probes require a stiff mechanism to get a reliable result. Any backlash/flex issues in your delta arms or carriages could be giving you issues (and could be a source of your dimensional errors?)
You can use the A & S parameters in your M558 definition in config to setup repeated probing to improve accuracy. I do this on all my printers, but would generally try and improve everything else first. Typically I use A10 S0.01 (so it keep probing until two results are within 0.01mm of each other and take the average of those two, but if it gets to 10 probes it just take the average of all 10)
Hope that helps!
