I would bet it is the Z axis that is the problem. it should be a negative number
I can use a lathe as an example :
usually the end of the part that is FARTHEST from the chuck is Z zero and gets more negative the closer to the chuck you go.
I think the mil is similar Z zero would be when the table and head are the FARTHEST apart then Z goes negative as you they get closer to each other.
try setting z at -4 and 0
Someone else will come along a confirm this I'm sure.