I agree that if you try to roll another boat, you should be prepared to be luffed. Hails are good practice, tend to prevent collisions, and support your position in the protest room, but (with the exception of rule 19) not part of the rules. As you say, the rate of turn is important. It has to be fast enough to be effective, but slow enough to give the other boat room to keep clear. That is a matter of interpretation, and whenever you go into the protest room over a matter of interpretation, you are in jeopardy. There is no "onus" in this situation. The only place in the rules that that presumes judgement one way or the other is RRS 18.2(e). Otherwise, the protest committee finds the facts and applies the rules based on them. If the PC finds that the windward boat capsized due to poor seamanship, then the leeward boat has not committed a foul. If they find that windward boat acted promptly with reasonable skill but was compelled to capsize, then the leeward boat broke RRS 16.1 and will be penalized.