honestly your biggest problem is your raid is oversaturated with healers. you can improve your numbers by snipping heals but generally you will cause overhealing on other healers while not giving anything back to the raid efficiency. you can try switching to earthen shield totem and grab some more absorbs. additionally you’re mastery heavy, which isn’t bad unless your raid is healer heavy like yours. most of your mastery is going to waste with your guilds raid comp.
either you should consider changing a healer or two to dps or hold out till heroic, when raid damage taken ramps up. Cant suggest much till then, sorry.