lilmod ulelamaid – Joe is known to cut and paste from Frumteens. That was not meant to be disrespectful to you, and I apologize if it was. L’maase, you were quoting someone quoting Rav Moshe, you did not (yet) look it up inside. It may be worth your while (as you seem to agree) to assume that the person (even if a Talmid Chacham) quoting does so selectively at best, or with and agenda. Look at the sources yourself and come to your own conclusion. Many Rishonim and Achronim quote others as support for their shittos, and when you look inside the actual source, they said no such thing.
As far as the Iggros Moshe is concerned, when discussing hair, there is no question that some prohibition is involved. Read the one that I brought earlier in Even HaEzer 1:69 discussing Da’as Yehudis.
I do not know Rav Ellinson (from whose sefer you quoted), but I will be Dan L’Kaf Zechus that he brings down both shittos. I will wait until you can do some more research.
Finally, I’m glad that you agree that 4 inches is not Halacha. A certain “Rabbi” supposedly put out a letter that wearing a skirt that is less that 4 inches below the knee is just as Assur (“no less forbidden”) as eating Treif or going mixed swimming. Then again, in the same letter he also said that you must have 3 inches of “slack” at the widest point of a woman’s shirt. It is critical to know what is Halacha, Chumra and Geder.
Being Dan L’Kaf Zechus, I assume the letter is a forgery, but some people really do think as such.