Our THC does something called Axis Override.. It uses a fake or false motor to handle the Jog velocity moves of your Z axis. In rare cases, some may want to have a separate Steps per Unit for their THC. When your THC tells Mach it wants to go up or down, you get this Axis override command to command Z in its stead.  All this logic is handled inside of your M3 macro. So when you call M3, it will start looking for the up or down commands after we have ARC OKAY and we get past to the "Cut" Sequence of the torch.

Do I have to edit the macro somehow? Or is the macro created on OB1 motor 5 and I just need to create motor 5? In the G code program, does the M3 command have to be called somewhere, or does Mach 4 automatically call the macro when the signal from THC up or down comes?

M3 or M03 is the same as turning your spindle on a standard system.

The same is done for Plasma, M3 or M03 should make the attempt to turn your Torch on.

Once your Torch is on and you have an ARC OKAY signal, your THC should work its magic.

In the configuration side have Motor2 set up as your Z Axis and have Motor5 enabled and setup as your OB1 Axis. Steps per unit, Acceleration, Max Velocity and direction should all be the same between the two motors.

From your TCH, you should have 3 wires coming to your Motion Controller (Sometimes this is a cable.) These three wires should be ARC OKAY, UP, DOWN.
Inside of your Mach Inputs Config, you will have 3 inputs available for THC. THC ON, THC UP, THC DOWN. ARC OKAY is your THC ON, UP is your THC UP, and DOWN is your THC DOWN.

These three signals control your Torch Height after the probing and Torch ON Sequence.

If this is set up correctly and you have the proper target voltage in your THC, you should have no issues with Torch Height.

By default on the plasma profile, you should not have to modify your M3 macro.

That's what annoys me the most about it. Everyone else does it without doing anything and I don't at all. I tried it now exactly as you wrote these settings and the result is the same. I'm attaching a video and a few pictures with the settings. I had to upload the video to storage because it's bigger.
video:
https://www.uschovna.cz/sk/zasilka/UWLX89CNLFAUWJZM-P39/

foto 01

foto2