Playng always the Romans , your question is hard for me, Constantius will be more detailed, ...anyway I would like to see more second rank cataphract Horse Archers!
I do not belive much in the full charge against formed infantry! IMO the Sassanian tactic was much more effective than the brutal frontal charge of the medieval European knights! A long prolonged arrows' fire then some charges, that could stop before the contact, if the enemy do not broke for the fear, then fire,... then charges, and so on.....until the final letal shock charge!
A refined and complex strategy, for experienced Extra Heavy Cavalry.
This is my personal picture of the Persian use of Cataphracts and IMHO the numbers and types of cataphract Horse Archers are somehow under represented,.......so,.. and here as a good Roman, I fear even the sound of my words

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I would see more Persian Cataphract Horse Archers Units!
Ah,forgetting! And again I fear what I'm saying!
More regional differentiation in the troops' choices!
