As I note at the beginning, take it all with a grain of salt, and ultimately exercise your own judgement.
That being said, the only situation where I'd consider not using Force Armor in rotation on the tank is during Kephess' final stages with two Sage healers in 8-man. There's nothing else in the game where I'd worry about spikes enough to deliberately exclude it. YMMV.
If we're presuming a high HPS situation (as Angel says, this is somewhat irrelevant if it's low-burden maintenance healing), refreshing Force Armor on the tank has some solid advantages:
2. It doesn't put Trance on cooldown.
3. It's more force-efficient than un-Conveyed Deliverance (which is going to have to be your filler otherwise).
2. It's an instant, which leaves you more time to NS/heal someone else. Ultimately you'll be doing more healing too.
I agree with your points, but it is my personal preference to heal up small damage with Rejuvenate and throw in a conveyance-HT if the health difference warrants that rather than just throw up Force Armor once Force-Imbalanced is off. Having said that, throwing down Force Armor as soon as I can does allow me to slack off on the healing to help dps or idle to regen force. For situations calling for high HPS, I do keep Force Armor up as soon as possible.
As you have mentioned, it's up to personal preference and deciding which way to go fits your playstyle and group more.