I'm not sure this is a bug, so I'm not putting it in the Bugs thread.
I've searched the forum and haven't found anything that discusses exactly this.
I guess the overriding question is this: What is the definition of Elemental Mastery? Is it having greater than or equal to 100 health at the end of a match, or is it having the health bar completely full?
The reason I ask is I've been grinding AI3 with an adrenaline-vamp-TU combo deck with pretty good EM results. I figured a SoD would help even more, for those occasions I've won with 95+ health because the AI dies before all my vamps heal me. Winning with the full 120 health yields a payout of 44 electrum, but if I win with 103 it gives me 21 (+1 for every 5 over 100). This makes it better to win with 100 than it does with 119. Is this an intended strategic piece of the game, or something that should be looked at and changed?