Situation 3
Personally I would hit the center (where it is weak) as hard as I could with full force. Rout the center and I think you're pretty much good to go...
It would depend on unit types though, because if it were a phalanx engagement it would take too long and the enemy flanks could swoop down and get you.
Situation 4
Move your forces offset to the left from the enemies. Hit them and curve move them backwards towards the hill. Even if they get rienforcement they're going downhill
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