It depends on your workholding solution, and the flatness of your stock:
- if you use top clamps, and/or if your stock is bowed or uneven in thickness, you should set a “large” retract height to be sure to clear the clamps while the machine moves from one point to the next. Typically 0.5 to 1".
- if you use side clamps and/or double-sided tape or tape & glue, the full top stock surface should be clear from any obstacle, so you can set retract height to just a few mm / 0.1" like in Ryan’s screenshot.
I would not go much below that (in the sense that there are risks of collision for stock of uneven thickness, and the gain in cutting time of reducing retract height further is negligible)