Hey lanarkmilling,
what you experience is a design flaw of the Z assemblies on all Onefinity machines:
Just be aware, that the more you slide the spindle downwards into the motor clamping mount to reach your workpiece, the more the leverage force exerted on the Z slider by the milling process at the end of the bit, the more your machine could encounter chatter or inaccuracy of results. Theoretically.
If you look at the position of the milling motor clamp on what I call the best solution for hobbyists and semiprofessionals who just want to plug in, the usual milling motor in Europe like AMB (former Kress) milling motor, the Suhner that is shown to cut steel, and the Mafell milling motor, you see the best position of the clamp: Directly where the axle comes out (note that you should not clamp there on your spindle. The Euro 43 mm motors have an all-steel motor flange. The manuals of spindles prohibit clamping directly on the bearings, the area where they are allowed to be clamped is a little higher on the stator sleeve).
Needless to say that with a Onefinity Z assembly, with such a milling motor, you will never reach any workpiece.
Unfortunately, I have no information about whether Onefinity has them on their radar and will provide an appropriate Z slider to use them with the Onefinity CNC.