Nerdiness
Just looking at the formula, since rotor radius is a variable the glide angle can't be the same for all helicopters. So the author's generalization doesn't seem to be quite correct. That's my interpretation anyway (and keep in mind that I rode the curve through calculus 2).
I'm a little surprised that drag doesn't factor into the equation, and that there isn't some correction for solidity of the rotor disc. What I take from this is that your sink rate increases with an increase in angular velocity (=rRPM, right?), and conversely it decreases with a decrease in rRPM. If you let your rRPM increase, you will sink faster; if you want to make it to a distant emergency landing spot, you want a lower rRPM!
Welcome to helicopters. They be addictive.