Yes, it is a right, of course, I'm not disputing that. All I'm saying is that it was the determining factor in me declaring war on Poland. Nothing more to it. Honestly, if I was successful against the OE, I wouldn't have declared war right away, but in the future I would have, just for retributions sake. But 2nd, I do blame Poland for my failure to stop your country. I publicly stated that Poland had my back where you to invade Europe, and yet Fnuco did not mention anything to me about the agreement being off until that hour of need. Yes, I do blame Poland, since Poland had signed a pact to help defend against Ottoman aggression. From my understanding of NAP and so on, it is usually good etiquette to keep them.
But here is the error in your rule, it will be shown most clearly. Ottoman Empire invades Austria in 1575. By this time, Astrakhan is under your control and Russia is your neighbor(theoretical). So now you declare war on me, and Russia sees the danger of you expanding even further and disabling me, and decides they will join the war to get Astrakhan out of you. At this point, Spain also joins to help Austria defend against this menace with 6 CoT and incredible economic capabilities. Now, we fight a grueling war. Hundreds of thousands of soldiers die, and for each country thousands of ducats are lost. Now, are you saying that all 3 countries, even though not in a formal alliance, can only collectively demand 3 provinces? This would be tragic for a nation like Russia who lost many troops and suffered incredible economic loss, and now is only able to demand one province if lucky. And if agreed upon by Spain and Austria, it could take a Astrakhan, but where does this leave Austria.. able to take one province after that long bloody war? After being incredibly weakened, taking one province would just be ridiculous, especially with France right on the border. No, I think this rule is harmful and would prevent just game play. This would lead to careless wars, since only three provinces is not such a crucial loss.