Respectfully, a refutation means quoting sources, not quoting what you feel the halacha to be. There has been more heat than light shed so far, so I thought it prudent to actually look up the halachos. Those here who are still oseik in torasu umenaso, feel free to correct me where I am wrong and add in additional mareh mekomos.
I read through OC siman 75 with mishna brurah last night and this morning. I also took a look at the aruch hashulchan.
Mishna brura makes it clear that all areas above the knees and elbows must be covered. The heter of less than a tefach of elbow only seems to be in regards to saying krias shma, not if a woman is allowed to walk around like that. Rav Shlomo Zalman Aurbach holds the elbow itself is like the area above it (dirshu edition notes). This point isn’t clear in the mishnah brurah. The Rem”a paskens that even less than a tefach is assur for saying krias shma if it’s not your wife. Aruch hashulchan argues on this.
The mishna brurah makes clear that there is no tzad heter for showing legs or arms if everyone does it, as they must be covered.
The mishnah brura also says that less than a tefach of the area above the knee is assur even if it’s your wife, since it causes extra hirhur. The aruch hashulchan argues, and says it has the same din as the arm. Rav Henkin quoted above says that less than a tefach of above the elbow is muttar lechatchila, but it seems to argue on Rav shlomo Zalman, who says the elbow itself must be covered even though it’s less than a tefach. Rav Henkin had a “limud zechut” (as in, “I hold it’s assur but perhaps they won’t burn”) if it’s more than a tefach but the sleeves are tight so the body can’t be seen. However, this seems to contradict the gemara which says tefach be’ish ervah. The Chazon Ish holds you need to cover from the elbow to the hand, but he seems to be a daas yachid on this. If there are any relevant igros moshes on it, please let me know. I hope to go to yeshiva soon to check them out.