On average raid boss fights, I try to keep PW:S active on the tanks as often as possible. While only tanks are taking damage, I spam Heal on them for low damage, Penance (try to use it on CD) and Gheal for large damage (for the healing as well as Strength of Soul) and then PW:S when Weakened Soul is gone. For group aoe damage, of course, PoH and bounce PoMs off of the tank. If you know someone in the raid is going to take damage (i.e. Omnotron's Acquiring Target), you can pre-shield them.
I also macro Inner Focus to Gheal and PoH so it basically gets used on CD.
Edit: Looking at your two specs, I noticed you don't have Rapture in one of your specs. Is that you PvE spec? But regardless of PvE or PvP spec, Rapture is a staple... Also, for non-heroic halfus specs, I completely ignore Evangelism, Archangel, andAtonement. They're not useful for most raid encounters and taking them makes you unable to take Strength of Soul.
This is my armory and my preferred disc raiding spec: I can't link yet. Char: Ellawell Server: Arathor (US)
I don't know if this helps but I usually have 40% or more healing done by PW:S on the charts and I top our healing. What are your stats like? I know I have +45% absorption for my bubbles and a good amount of Spirit. Also be sure to time your spells and Inner Will + Power Infusion = 3500 mana cost PW:S spam.
with stacked mastery (16,8%) on fairly low crit and really low haste (3%) you actually would be best spamming bubbles and speccing with sos
i get the impression that your spec dont fit your stats choices.
if you like to smite-heal and avoid shields you would be better with perhaps more haste instead of mastery and maybe darkness instead of inspiration.