That sounds like kind of a nuisance sort of problem, almost like the setup parameters are not quite correct. I would think the machine should find its Z index on startup, call that point Z+4.8566 (via an internal parameter setting which would define the position), and then move to G53Z0 as the last step of the homing routine.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)