Does convalescence stack with defiance?

[TheodoreMcIntyre]

Yep. Can't recall if it's multiplicative or additive (though I thiiiink it's multiplicative) but you'll get higher heals with Conv + Defiance than you would purely with Defiance.

I want to say they're multiplicative, because defense buffs are, but that would result in more healing than additive, so I'm not sure. I know for certain they stack, just not really how.
With Defiance and Convalescence, if it's multiplicative, Defiance + Convalescence gives you +44% healing, as opposed to 40% if it's additive.
In conjunction with Fey Illumination, which is also 20%, this makes the buff 72.8% to incoming healing assuming multiplicative, as opposed to just 60% if it's additive.