Becuase when you hear the word empire I imagined they controlled a large portion of Ethiopia then invaded yemen. Bu if you look at thr map it becomes clear how close the section of yemem they invaded and controlled is.
The thing that misled and confused me was Mani supposedly touting Aksum as one of the powers of the world. Back then I instantly assumed it must have been big and comparable to something like the Iranic Empires and the Greco-Roman Empires.
In reality, it was probably just notable given it was in control of a chokepoint of trade along the Red Sea and could influence global commerce that way but otherwise it doesn't seem to me that they controlled much beyond Northern Eritrea, the Tigray region, maybe a bit of eastern Amhara and then parts of western Yemen and Sudan during conquest periods like Aezana's which didn't exactly last as generational holdings.