I dont know If I mentioned this, but the Seleucid heavy phalanx looks identical to the Macedonian heavy Phalanx.
I looked at the other factions and the Thracian Pezhetairoi would suit the Seleucid Empire perfectly. Im not a history major or anything, but did the Thracians actually use Pezhetairoi Pikeman? I cant find anything about it, but I think their phalanx model looks like it would fit in better with the Seleucids then the Thracians.
I dont have time to post a screen atm cuz im about to head off to report for duty. But set up a custom battle Thracians vs the Seleucids(this is what I did) and just do a phalanx vs phalanx battle and youll probably see that the Thracian phalanx looks wya more suited for the Seleucids.
Just my two cents.