Eye of Sauron, jeeze that thing came make ambushes almost useless.
Well they may actually work if you don't 'hide' your troops by walking them toward the enemy through the edge of the forest closest to the enemy.
I mean, seriously who fights with cav by frontally attacking Principes & Triarii in a forest?
Put the cav on the far side of the forest until the enemy has gone past, hide the left flank actually deep in the bit there but don't try to pretend that the AI finding those shallow hidden troops was a sign of great AI.

Worse, the Roman army when initially spotted seems to be moving toward the cav in the forest -> knows where the hidden units are & is heading for them, not 'trying to sneak some units through there'.

Back in Shogun1 initially the AI didn't know you had hidden troops & you could actually do ambushes which was good.
Then they patched the AI to count how many units were visible & if it couldn't see all the units it would go hunting forest bits for them -> ambushes became pretty much impossible.