Playing as Prussia, I have Brandenburg as an ally. I have a marriage, an alliance, same dynasty, "we are kin" rep bonus, "consort ties" rep bonus, we are both protestant, we are both members of the HRE and 100 trust with them. However, when the Brandenburg king dies the game has decided that Poland should be the country that gets the claim on his crown. Poland is catholic, married, but no longer allied to Brandenburg, lost a war to Brandenburg and myself, and the Polish king is a queen with average legitimacy. My legitimacy is average as well, but all other factors considered, common sense would say the "math" should award the PU to me to defend, not to Poland where I have to challenge the PU.
Am I missing something that counts towards PU's not listed above?
Am I missing something that counts towards PU's not listed above?