I could b e wrong on his actual percentage. Based on how the warforged healers friend stacks up with their normal 50% amp. But that doesn't mean I'm wrong about how healing amplification multiplies and does not add. Consider the poster claimed he was easily at 10% because his numbers added up together I'm not inaccurate.
I'm assuming his logic was 50% + 15% (healers friend) + 10 (finger necklace) + 10 (docent) + 20 (ring) = 105%
The above is not currect. If healers friend is added then it could look potentially like this:
.65 x 1.1 x 1.1 x 1.2 = 94%
There isn't a definitive answer on if it does and according to the wiki it's muliplied in a certain manner.