They have their gimmicks—tank switches, running away with fire beacons—but none of them that apply especially to holy paladins. All are brief encounters.

Raid damage is much lighter in P3 physical realm, but the tank damage is also much greater in the shadow realm (or whatever it's called). I don't know about assuming you should be sent up to the physical side.

Assuming you are running 2-3 healers (my guild runs 2) you can't afford to stay in shadow realm. There is too much movement and you won't be able to keep up your holy lights when you have to move out of the cutter. Physical realm is a much better choice for holy paladin healing, plus the FR aura is quite helpful up top.

As long as Coporality is maintained, actual damage against either tank is lower but the danger to everyone else is a little greater (void zones give a slow/snare debuf). In any event, there is a lot of movement in the Shadow World where I never felt as effective. I definitely feel Real World is more appropriate for Paladin healers.

Assuming a holy paladin is bad in the twilight realm because of movement is being ignorant.

Even with defile/vile spirit/valkyr movement paladins remain the best tank healers on Lich King.

In reality a paladin is very well suited for the twilight realm. The entire raid is grouped up so GoHL will heal for tremendous amounts. Movement during cutters doesnt limit your HL usage as much as you'd think.
You can squeeze out two HLs before having to move again. During that time you have HS + IoL FoL, which covers the 2 GCDs it takes to get in a position to cast another HL. Plus the spot healing you can maintain on the Soul Consumption taget while still healing the MT is perfect. This applies to the upstairs world aswell however more healing is needed on the Soul Consumption due to the aura ticking aswell + a potential slow if freedom wasnt applied.

I just think that the notion of a paladin not being a very good mobile healer gets overstated sometimes. We arent good mobile healers, but if a fight does require movement I dont think it automatically disqualifies us. Think LK again.

The Statement that "Paladins NOT being a VERY GOOD mobile healer" cannot be overstated. You yourself say so in the next sentance.
What might be considered an overstatement is Paladins are VERY BAD mobile healers, but even this is arguable.

Given all that it would be an unusual healer team that would put their only holy paladin in the twilight realm.
But against that just because you have an oversupply of holy paladins does not necessarily mean you have to call it rather than have one of them helping in the twilight realm. I just think you are "Overstating" your position

I was speaking of 25man.

At first we did place our pally up top, but decided to have her come down after a couple attempts ending in tank deaths. The damage up top is relatively trivial. I believe we ended up having just a Shaman and a single tree up top in the end. Our pally was annoyed at the movement required down below, sure, but she still managed just fine. That change ended our string of wipes due to tank deaths.

Paladins may be bad, or even horrible, mobile healers, sure, but the point I was trying to make is that they're still more useful down below where the damage all around is much more intense compared to up top where it is relatively light.

On LK Heroic I only use RF when we have our DK tanking the adds in P1, I had too many instances of loose ghouls aggroing to me with other tank set ups.

When solo healing the physical realm on RS 10H P3, we had an elemental shaman offhealing when I was marked and had to run which pretty much solved all the issues we had with that part of the fight.

Ghouls aren't a big deal, even if they get on you it's not like you're going to die, and the tank can taunt it back anyway.

On a new subject while getting bored farming ICC I decided to try out the FoL build having regemmed full sp, reglyphed, and changed my gear setup. I was running with 801 haste (which I do realize is a bit much), 3551 sp, and 42% crit. Remember too all those stats are completely unbuffed, also running 2p t10.

Here are the logs for the night if you're interested in looking. World of Logs - Real Time Raid Analysis

My stance on the FoL build is to stay far away from it for the rest of this expansion. 1sec 12k casts (in raid with 25% ICC buff too) vs 26k+ HLs on a 1.3sec cast speaks for itself. Spamming FoL on 11/12 in ICC it likely won't have that big of an impact due to the state of how easy 11/12 are with the zone buff. However when it comes to H LK where it counts you obviously cannot rely on FoL to keep tanks alive. H Halion would be a painful encounter as well trying to keep dragon tanks alive through corporeality fluctuations and add tanks when they spawn.

The good thing about the spec is mana should never, ever be an issue unless you start to spam HL heavily. Overall I would never recommend it for a serious spec.

I would reconsider how your overall raid is positioned, if you tank facing the outer ring and have the raid swap one every meteor crash, without the addition of adds in 10man this makes it a lot easier. By going to this strategy you will, be able to reduce the build of additional stacks by running the Mark of Combustion directly behind you to the outer edge. Depending on raid comp, the upper phase is usually composed of ranged(spriest, bookin, ele), each of which have the ability to heal. Would be in your best interest to call for some type of heal or something if you really need it; if not save your DF and HS with a Instant FoL and heal off of yourself till the debuff wears off, but you should not reach past 3 stacks before a dispel.

I would hold off on RF till later phases, in phase 1 depending on RnG you might pull a ghoul with a building stack and have necrotic plague be passed to you, in this case you will be forced to run to the OT causing unnecessary movement(and possibly a tank Gib depending on your other healers), I would just wait till P2 or later to activate RF.