Why not just allow both?
Zone of Control: As an action, you can choose area or a target creature. If you choose a creature, your zone of control extends 5' from the target and remains centered on the target if it moves.
At level X your zone size increases.."
So you can say "I'm watching the doorway." or "I'm watching the dragon."
Hmm. There are advantages, but also disadvantages, to the idea.
Let's look at the cantrip-like abilities that are predicated on it being a fixed region, rather than tied to a person.
1) Enemies can't make opportunity attacks (OA) against allies moving out of the Tactical Focus area.
If you target an enemy, it mostly means that that enemy cannot ever take opportunity attacks. But it also limits the scope of your ability to provide a safe channel for people to move through, to escape an area of enemies. It feels like a weaker choice.
If you target an ally, it gives them freedom from all opportunity attacks (if you even allow it to work when the ally is never moving 'out' of a given region) for their entire movement. It feels like possibly too strong of a choice?
2) Hitting an enemy in the TF area can be moved 5'. (no saving throw)
If you target an enemy, this means you can perpetually move them on each hit, since the region moves with them. This seems overpowered at first thought, but then again, you can do the same thing to a selected enemy if you shape the region correctly, for up to 4 attacks. It just feels a bit cheap in that you can knock the enemy back any which way without any planning associated with it.
If you place it on an ally, it means basically anyone they hit, they can knock back. Again, it's possible to make this work with the region definition, but it feels cheap without it because it doesn't require any planning. Just tell the barbarian to go hit that guy. It seems to lose the sense of being the tactician.
3) Ambush: As a reaction (by the Warlord) when an enemy enters a TF square, you/allies may move half your speed. Does not use allies' reaction.
This has no real use when placed on an enemy, since they'll always be in the TF square.
If you place the TF on an ally, you get the same effect as if you had placed the region next to the ally, waiting for an enemy to approach them to within melee range. It does require you to figure out which side is their weak side, though, since you can only cover half of the area around them.
4) As part of move, can swap positions in TF area using 10' of movement.
This appears to be pointless for both setting the TF on an enemy and on an ally. The advantage of a position swap is being able to move people several squares at once; they can be up to three squares away from each other.
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Most of what you can do when targeting an individual can be done using the region definition. There are a couple things that don't work quite as well going in the other direction. The
feel of how they work when arranged in a region vs targeted on a creature, though, feels more like tactics when in a region, and more like a buff/debuff when targeting a creature.
Targeting a region is more difficult in Theater of the Mind settings, but far from impossible. Target a band between your allies and the enemy. Create a strip through the enemy line that gives an exit route. Focus on this area of the hallway, or the region in front of the door. Focus on the area the boss is standing, and the area behind him leading to the cliff. Just adding some mental 'space' seems pretty sufficient.
If we can think up more ideas of things we can do with the TF area, though (ie: more cantrip-level gambits), it can help define whether creature-targeting is useful, or whether it detracts from the design concept. I'll try to come up with a few.
