Sam2,
You are misreading the nosei keilim. Less than 4 amos is a middas chassidus, more than 4 amos is required, because that is the minhag. It is true that originally kisui harosh was middas chassidus but the minhag was already widespread enough in the times of the Shulchan Aruch that it was binding.
B’ezras Hashem, tomorrow morning I will explain why Yitay is wrong in his reading of the Gemara and his kashos on my pshat.