What is the highest safe Z height?

I am finding that anything above 2" doesn't seem to work, when the Z makes it second slow plunge and reaches 2" the machine errors.
Is it possible to set the max safe Z height to anything above 2".

I ask because I cut a lot of 3D files (3"-4" tall) and would like to zero to the table, however without being able to set the safe Z height about 2" I am not able to zero to the table and then clear the material.
Am I going about this wrong, or is there a simple setting to allow higher safe Z heights?