Crab,
You over look that "rule" applies to the over taking aircraft as well as the one being overtaken.
For sure unless we have eyes in the back of our heads and the ability to see around the airframe....checking Six is a bit hard.
Nice bright Strobe Lights and brightly colored airframes with hi-vis painted rotor blades are about the best we can do along with TCAS and other aids.
I'm not overlooking any rules - if the overtaking aircraft can't see the one ahead (often because it is slightly below) then all the strobes and coloured blades in the world won't help.
In modern aviation, transponders and TAS/TCAS should be mandatory, even in class G - as we are seeing more MAC, lookout (good as it is) is often not enough.