I know that its probably somewhat hard to program this in a satisfying way, since if they just run away as far as they can it takes ages to catch up with them.
But currently it happens way too often that enemies that have a clear way to escape, instead run away for 1 turn, and then back in the next. This often results in them running into some kind of AoE effect (e.g. spirit guardians), effectively removing their turned condition. If its too hard to make the AI NOT run towards the player, just let it run away a bit and then take the dodge action (see the official turn undead: "If theres nowhere to move, the creature can use the Dodge action."
Im playing the game on the highest difficulty, and nothings more frustrating than having to restart an encounter, because all 3 enemies that got turned last turn, decide running away is for cowards and move precicely into my AoE effects (of course, I could not use those effects, but thats more of a work around against something that shouldnt be happening in the first place).