Most of the times in the top there are 1 HP decks because the day before they were about 65 or less, yesterday I happened to meet two of them while testing a deck in gold (lucky ^^), both at really low HPs, and won against both, that's why I wanted to account that. What's more, it's not like they're decks built by superhumans, simply they had a giant MU against the main decks used to farm, that's why using an unused deck I could kill them, it wasn't expected.The best way, probably, to account them is to make an average of the rewards, something like: [average electrums per win of first deck+average electrums per win of second deck+...+average electrums per win of tenth deck (IIRC, though, the tenth deck doesn't have multipliers on it, but let's just say it has till we can get our hands on the real values of the multipliers)+(average reward of regular wins*490)]/500.
The problem is that it'll increase, even if by only a little, your electrums per hour, but if you get two of them like I did, it'd be awesomely off. Oh well, that's the problem of calculating the UEI of the Arena in general, it has too many random factors.