Quote Originally Posted by Saeleyna View Post
Pretty much this. If you're (vice)MVP you get more. Not sure exactly how the numbers work but contributing more to the fight = higher chance to get multiple souls.
I haven't really paid attention but... MvP and founder rewards are all Platinum chests, and I don't think that aside from the (non-100%?) founder one, I don't think any of them are Platinum?

So, I don't think that there is any correlation to how well you place in a raid. It's just RNG.