*Fixed*

So in the end this was just a silly misunderstanding from me about what the leveling-strategy.three-point-leveling.tolerance value was for. I had upped it to 3mm (default is 0.03mm) and that just meant it ignored the un-level bed because it was within a 3mm range. Changing that back to 0.03 means it now works as soon as G32 is complete. That also means some of my ideas about needing the flag ZHome were just plain wrong. You can simply home in XY, and use something like G30 to establish a Z starting point for your prints.

Big shout out to wolfmanjm on the #Smoothieware IRC channel who helped me track this down.

I'm having an issue with auto levelling using a 3point z probe plane.

I have a cartesian style printer and use a BLTouch as my ZProbe but do not have a ZMin or Max endstop

My process at the moment is roughly as follows:

G28 (homes X/Y)
G1 Z10 F1500 (move z up a bit in case it's too close to the bed for the BLTouch probe)
M280 S3 (drop the probe)
G4 P100 (wait a bit to let the probe settle)
G32 (perform Z probe - 3 point in my current case - auto save on so I skip M500. At this point it shows the plane it's saving in the log)
M280 S11 (retract probe and turn off any warning that might have began)
G1 Z10 F1500 (move up again)
(I'd probably only do this first part every time there's a change to the bed/printer)
G28 (home X/Y)
G1 X90 Y120 F3000 (move somewhere sensible to find Z)
M280 S3 (drop probe)
G4 P100 (wait a bit to let the probe settle)
G30 Z1.1 (find the bed and set the trigger point to a Z value based on nozzle distance above the bed when it triggers - effectively sets Z Home/Z Zero)
M280 S11 (retract probe and turn off any warning that might have began)
G1 Z10 F1500 (move up again)

So at this stage I can begin a print and it'll start at the correct location etc. However, I'm not seeing any changes in Z as the head moves in the X/Y (which is what I'd expect to see as the bed is definitely un-level)

Following the cartesian section of this guide: forum dot smoothieware dot org/zprobe#toc19

I notice that they have an extra step of moving the nozzle head to the first probe point, manually moving to a good Z height and then use M306 Z0 to set ZHome/Min. I can't do that bit as my Z Home flag is not set so the M306 command fails. Instead I set Zmin with G30.

Should I be seeing auto levelling working with my process as is?
Am I missing a step in this process?
Is there a way to manually set the ZHome flag and then use M306 Z0?

Edit: I think I've made some progress - it looks like my OS (Mac OS) was auto mounting the SD card and blocking the eeprom write after doing a zProbe giving me a 0byte config-override file. However, after making sure the SD card is not mounted and running the plane probe I do get a 1KB override file but I'm still not seeing any changes in Z height to compensate for the un-level bed.