I'm pretty sure it's not possible to have 120+ units on large unit size.
And increasing the Triarii unit size is not historically warranted. In fact, they're innacurate now. In fact Triarii maniples contained only half the men compared to Hastati or Principes maniples (60 instead of 120)
So it wouldn't have been possible for the triarii to form a long, Greek style phalanx because they wouldn't have the numbers. Their job was to form a core of fresh veterans who'd stop the tired enemies long enough for the principes to reform for another attack.
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