Once the force went low level the FF Vulcans would have been hard pushed to cover Moscow and as far as I am aware any coverage would have been the Blue Steel Victors and Vulcans - with 5 aircraft on QRA.
Moscow was well within the range of the FF aircraft and remained an allocated target until well into the 1970s. Given the "Moscow Criterion" that's not really surprising. Now whether it would have been a primary target for QRA FF aircraft is another question altogether; one to which I doubt we will ever know the answer.
Of course the aircraft was the back up if the Blue Steel went U/S - very sporty doing a popup attack.
Not dissimilar to the YS2 "low level" profile. IIRC both were designed around the SA2 parameters; the missile would hit you about 20 seconds after weapon release! The survivability quotient for was pretty low, but by that time did it really matter?
exmap