I believe this is best addressed by case 93 or, better, by case 146. There is no protest on this situation at all.
While racing keel boats under PHRF, in about 12 knots of wind, I was approaching the starting line with about 15 seconds until start. I was burning some speed by letting the headsail luff a bit. Another boat approached from clear astern and started yelling "up up" as they are want to do. We were both on starboard tack. This boat had no lookout at the bow and was a 30 foot boat (I'm sailing a 35 foot boat) so I doubt he could have seen exactly where his bow was. From my position at the helm I could clearly see that he had not overlapped me and, if he headed up, would have easily crossed my stern so I took no action. About 5 seconds later he did establish a slight overlap, about a foot or so below my starboard quarter. Had he headed up he certainly would have contacted my boat. I had space above me but had I headed up, I would most certainly driven my port quarter into his bow. If I bore down, well that of course would be bad.
I can't think of any action I could have taken to avoid him and allow him to head up. He began yelling "protest, protest" although he never flew a flag and ultimately didn't file a protest. He was of course right to avoid contact.
1 - He established a leeward overlap from clear astern
2 - He is obligated to initially give me room to keep clear
3 - I failed to keep clear, because it was not possible for me to do so
So I think I was sailing within room I was entitled under 16.1 and therefore are exonerated under rule 21.
Is my analysis correct?