What is important is that the cutting/engraving plane stays the same as when you did the calibration. For example, it is ok to drop the cutting bed 8 inches to engrave the top of an 8 inch thick box since the cutting plane will stay the same.
Some lasers have an easily movable focus tube that you can slide up & down instead of moving the bed. If you do that, it changes the distance from the focal point to the camera. If you use the Z-table to adjust the height, everything is consistent and there’s no issue.
Yeah I don’t think I have the moveable focus tube. I have a 28"x20" blue/grey Chinese 60W. It turns out I bought the wrong camera as well. I bough a 5MP / 60 because I thought it would be high enough above the bed. Unfortunately, when I measured between the open lid and the bed, the bed was lowered all the way down for my rotary tool. I have now ordered a 8MP Camera (4K-N) which will be mounted about 29" above my bed so hopefully I can get everything going this week.