oooh! I'm researching some related issues at the moment. The depiction of the Ethiopian agemata is based--I think--off of artistic depictions of them. They should probably be called "Trogodutai" rather than Ethiopians, since that is what they are called in the papyri. I haven't seen full evidence that they were given land allotments (thus becoming klerouchoi), though they may have been given some sort of settlement incentive. The few things I have seen on them have them fighting rebels along the upper Nile. I don't know if they were even really hired until after the first major rebellions (which followed Raphia). Perhaps the EB team has a historian who has done more work on the Ptolemaic military than I have at this point, and could give you some more info.
Now, as a counter example, Harkonesis, a mercenary horseman in Pathyris, in the Fayum, sold (in about 109 BC) a fourth of his government land allotment (sounds similar to the klerouch arrangement, though it also seems he is still in active service, so its complicated--perhaps it is inherited) to make a grain payment. Now, he's identified as black-skinned, and therefore broadly defined as "Ethiopian," but beyond that, we don't know much more about him (he's also very big), except he almost certainly wasn't one of the axe-carring agemata, in whatever form it may have existed.
So while I can't say specifically what EB's Ethiopian agemata was doing, and how they were recruited, I will say that many Galatai, Trogodutai, and Thraikoi were recruited from military settlements along the Nile. Even with the Galatians, many of them were probably recruited from the epigones (military settlers) and possibly klerouchs (more wealthy military settlers). However, I'd like to see some evidence Galatians were klerouchs, most of the few I've located in papyri were epigones.
On that note, where are the Thraikoi klerouchoi? They are far more visibile in the sources than either Galatians or Ethiopians.
And on a note for my own interests, what sort of visual sources did you EB guys use in figuring out the Ptolemaic armies? There's a gaesatae figuring from Alexandria in the British museum...perhaps there could be a way to recruit them in Egypt, or at least to go pick up a group of 'em in Anatolia?
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