anti dive in MACH is based on the actual speed and will not work if the speed does not slow down during the cut. It's primary design is to keep the torch from diving on sharp angles and at corners where motion feedrate drops below a set percentage of the normal feedrate.
There is a way to turn off the THC function in mach but you will need to have an M Code macro you can use in the G-code. You call the internal function in MACH to turn the THC logic off or on but they only way is to pass it the function call in the g-code.
The best way is to do the anti dive dynamically (based on the actual arc volts) rather than feedrate.
Our new MP3000-DTHC has that feature (we call it a "tip saver") because it keeps the torch from diving if you pass over a void or come back close to a lead-in. The operator can "tune" the value in the dynamic Cut Profile for each type of material they cut. The difference is that it does not disable the THC in MACH so if it still needs to raise the torch it can. Once the condition returns to normal the THC resumes normal up and down movement, It just keeps the tip from slamming down on the material.