"So divide your Rrpm by 60 and see how susceptible you are."
Wouldn't that only apply to a single bladed rotor? Surely you need to multiply that by the number of blades, as that's how often the sun is going to be blocked, per second?
Where does your figure of 17 for a Huey come from? using your calculation you imply the RPM is 1020.
Interestingly, though, I find the 155 gives me some uncomfortable effects sometimes if looking through the disc or at the nav log and the sun is directly above. If your flicker range is correct, then this ties in as the 5 blades and 342 Nr gives a frequency of 28.5 Hz.