Now I've looked at the Surface X/Z probing information again, I realise it's just doing a perimeter type probe but in X/Z.
I thought it was doing a bed of nails type thing within a perimeter.

I'll admit, I don't even have the latest version installed, as I've got no need for that feature. As with anything Mach3 related, I opt for the, if it's not broke, don't fix it option.