The A319 has the longest range in the (non-neo) A320 family, not uncommon for shorter-fuselage versions: they’re the same basic designs, but the shorter versions weigh less. (The 737-600 also has the longest range of its generation of 737s and the 737-700 the second longest, for example.)

Say what you want about AA, but you can be assured that they don’t fly aircraft models that don’t have the safe range plus safety margin for the routes they’re assigned to.