Thank you, everybody. Our flight back from SXM to PHL is (surprisingly) direct (for time being). Don't know why AA changed formerly direct incoming flights to stop (and change planes) in MIA.Returning through Miami, it will be the same as any other return to the US. At the port of entry (Miami in this case) you must clear Immigration, claim your bags, and clear Customs. If you have a connecting flight then you must recheck your bags and clear TSA security before proceeding to the gate.
Probably to insure a full flight......