Not having a pop at you it's just that Mach works different ways for different people.
It's a complex mix and computer and machine.
Couple of years back i spent a whole week doing nothing but threading and reporting back to Art, try a new driver, rinse and repeat.
It's not a question of a nut having 1.5 to 2D length but more about the thread deteriorating over it's length and believe me a piece of al thread is accurate enough.
This is a classic example.
just two passes but you can see that after the first short length it's starting to go out of pitch but different error on each pass with the result that the last bit of thread is useless.
It's all down to the single pulse, Mach can't use a multi line encoder [ yet ] so we are stuck with it and it is the pulse.
EMC can use a multi line encoder and it threads perfectly and accurately.
I use my cnc for some threading production jobs but they are only 10mm [ 3/8" ] long and they come out OK.