What units is the most effective in auto-resolve for its upkeep?

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I want to construct an army (and fleet) that will be the most effective in auto-resolves for its upkeep (ie. there is no army that can be constructed that can outperform it while not having higher upkeep). I'm playing as Rome.
How can I do this? Are there any rules that the auto-resolver follows? What is the optimal composition?
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Auto Resolve Guide - Total War: Attila
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