Some minis (depending on when manufactured) have slight variations in measurements due to part changes. As a result, some older minis don’t reach the wiper/washers as they should with new firmware. The older firmware (1.0.xx) also had a bug which made it go 1mm lower for any given Z position than current firmware does.
There are a couple of good solutions to the behavior you are seeing…
(1) Add an G92 command into your start script. Right after the initial homing command (G28), add a line with “G92 Z160”. This will tell the printer it is at 160 instead of the firmware default 159 when at the home position, so when commanded to go to 0 it will move down 160mm instead of 159mm. You may need to use “G92 Z161” (to go 2mm lower) if the Z160 is not enough (depends on your printer). You will need to check/ensure you have this command in your start script whenever upgrading to a new version of Cura, or using a different slicer. And of course you want to remove the G92 if you revert to the old 1.0.xx firmware where it isn’t needed.
(2) Glue or tape small shim (1-2mm in thickness) on the inside of the top frame, directly above the Z_Max limit switch. This will cause the switch to close 1-2mm sooner, so that the default Z_Max_Pos of 159 will be correct. The advantage of this approach (vs the G92 method) is that it corrects the problem through hardware, so you don’t have to worry about maintaining a script change in future versions. Just be sure to remove that shim if you revert to the older 1.0.xx firmware.
If the nozzle does reach the washers when probing, and the only problem is reaching the wiper, then you could always just change the Z coordinates in the start script lines responsible for the wiping. But this requires changing several lines, and doing it every time you get a new version of Cura with new start scripts – so more work than the G92 method where only one line is needed, and more work than the “shim” method which requires no script changes at all.
Yet another method is grabbing the firmware source, changing the Z_Max_Pos declaration to 160 (or 161), and recompiling. That’s not terribly difficult if you have a little programming background, but the above two options are a lot easier – unless there are other firmware customizations you want to make.