In my opinion the preflight will turn off (M71+M70, with M70 as the last command), and RFH will turn on (M71).
However I believe Hood would be in a better position to tell whether your constellation is run correctly from Mach3's point of view. (correctly sequencing the several M70 and M71's in the preflight)
I could imagine your external device does not like (enjoy) M70 and M71 within the same millisecond. You could try a dwell G4 as the RFH point, just before M71.
PS my manual reads: "Run From Here performs a dummy run of the program to establish what the modal state (G20/G21, G90/G91 etc.) should be..." I'm not sure if that is in the offical Mach3 documentation therefore I post it here.