Not quite sure what the Dominion bonus is. It seems to get smaller the more dominion I play, or the longer the game gets.

Anyone know what the idea behind this seemingly arbitrary number is?

From what I've been able to gather, the "Dominion Bonus" seems to be based on how well your team did.

It seems to be based of the remaining health of the winning team's nexus. such that if your team won, and you had a lot of health left on your nexus, the bonus can be as large as ~+20. On the other hand, if your team LOST, but the opposing nexus only had tiny bit of health left, you earn a large bonus as well.

The low bonus means you either won by a very small margin, or lost by a landslide.

Ah, so it works like the Long Defense and Quick Victory IP bonuses of old for SR. Thanks.

I just got 7 for a 19 minute game.

In regards to it being based on team score, for reference: We had 314 left on our Nexus. Team scores were 1310, 1213, 1183, 1173, 958.

It also seems to be somewhat based on your personal score, or possibly your position within your team, such that higher score gives you a bigger bonus.

No idea if it's just score though, haven't had enough games where I end up low on the ranking but with a lot of points to check.

What if it's based on both nexus health and time?

If you get more dominion bonus for shorter games, it's still better to hold 3 positions for a longer game, since the regular time IP bonus if larger than any dominion bonus I've ever seen.
If you get more dom bonus for longer games, strategy the first is even better.