We have a trip in March, booked with AA, economy saver fares. A leg of our trip is Birmingham UK to Dublin, on Aer Lingus. We are concerned about baggage sizes. We will each have one carry-on and one personal item that meets AA requirements. I've been reading and see that Aer Lingus personal item size is much smaller than AA. Since our tickets are booked with/through AA, will we be subjected to the Aer Lingus baggage requirements or do they have some type of agreement? Could we pay to check our AA carry-ons as checked baggage on Aer Lingus, then our personal item would become our carry-on? If so, how would I go about doing this? We are traveling in four weeks and I want to get this all figured out before then! Thanks for any help you can give.

(Edited to add that I have also posted this question in the AA forum)