Regarding the Z-axis issue

NEJE MAX 4 V2 E80， Equipped with Z-axis stepper
I am trying to set lightburn so that when I input the material thickness, the z-axis will move to make it in focus.
I have set the G54 z offset to -17, which is the focused position on the machine tool.
When lightburn runs, it raises the z-axis to the height of the material, placing it in focus.
My question is that the beginning of lightburn gcode increases the z-axis in relative mode based on material thickness. For thicker materials, if it exceeds the limit, the z-axis will also exceed the limit.
Everything works as expected in absolute mode, but not in user origin mode.