Sasless has long said Robert Mason borrowed others experiences without attribution and had an amazing inclination to embellish thus making an account loosely based upon a modicum of truth into a good yarn. I have a dear friend who shared a Cockpit with Mason on occasions and I trust his evaluation of the matter.
That being said....the UH-1 in those days had Standard Nav lights that could be selected to Off, Bright, Dim, or Flash.
Bright was standard.....Dim were really Dim....like about as bright as your standard two D Cell flashlight (Torch) when you really....really need some light in the Cockpit when you experience a complete electric failure. The flash mode was at the normal bright level. We had no strobe lights but did have Rotating Beacons.
Day formation, while in the left seat.....at one half rotor disk separation....one could leer into the right hand door window of the adjacent aircraft and see the instruments. In those days we could actually see the indications of the VSI and Altimeter.
We did not overlap blades routinely or on-purpose normally although sometimes young men who have scant sense of their own mortality will do some very stupid things.
At night we maintained the half disk to one disk separation......the same peek in the other cockpit might yield a dim red glow but that would be it as we ran our cockpit lights as dim as possible to enhance seeing something outside.
Generally....Lead and aTail end Charlie ran anti-Colls but on approach those got shut off.....leaving just Nav lights on.
The Nav Lights were blanked out when viewed from below....as we wished not to be seen from the ground.
To clarify....once on Chinnoks...everything was the same except we went from half disk separation to half day separation generally as my unit generally did single ship tasking but when the opportunity presented itself we ganged up and postured upon returning to base.