I believe someone said (i think Eddy) earlier in this thread that the tooltip hasn't been "fixed" but the actual amount of attackpower gained has been.
On 10 man it's 30% of max hp, and on 25 it's 50%, so reaching anything above 30% of your max hp is just a tooltip error.
If i'm wrong here i'd love to know but I believe this is how it is.
As for you santa, 556 is indeed pretty damn low
kinda suprised you're that low really, i'm thinking 3 healers two tanks personally, 4 healing route i'd never take. But if people say 1 tanking it is easier on everyone then ye... would be a bit silly not to.