If you were CoH only (especially since it's getting "nerfed") then I think you might need to be concerned.
However, in a 5 man... Overhealing doesn't matter.
In a Raid (25 man specifically) it's a little bit bigger issue, only because it's harder to overheal a LOT and still not run OOM.
Either way, 11.5% isn't a lot. If you were in the 20-30% I'd be more concerned. 11% is pretty decent.
Either way... if you're responsibility stays alive.. OH isn't as big of a deal as some other things. It's always a good way to gauge how slow of a reaction you have (compared to other healers in raids).