I don’t have an answer to your primary question, but an observation regarding your power settings. Do you know your safe maximum power setting, based on testing with an ammeter and a reference specific to your tube?
It’s understood that power ratings for laser tubes are exaggerated by marketing forces. My 60 watt tube is listed as having a safe maximum power of 28 ma draw, which translated to 65 percent (the last time I tested).
Exceeding the recommended rating will reduce the life of your laser tube.
Of course, considering that you wish to cut thick wood, reducing the power to increase the tube life is going to make the job a bit more challenging.
If your machine has on-the-fly z-adjust, your changes make sense. You’ll likely get charring along the previous cut depth, as that portion of the beam will be out of focus and wider than at the focus point. You also could check if starting at the 0.25 offset will cut deeper, but you’d have to slow the speed even more.
0.2 speed means what in the real world? For thick stuff, I use 5 mm per second, a reference of distance per unit time. If the speed is mph, 0.2 mph is about 90 mm per second, a good speed for engraving tough material.