So I've been playing mostly dominion the last couple of weeks and I'm loving it.

When my team loses I'm usually near the top of the placing board, when we win I'm on average a bit lower. 4th - 3rd rather than 1st or 2nd. Does placing matter at all?

I can see how just being a harasser and defender can really support your team but might not give you as high of a score. At the moment I'm doing so well because I'm getting a lot of assists, captures, and some kills.

But is the scoring system accurate to how much people participate in the victory or loss?

sort of.. I play assassins in dominion and I end up with less points, because I usually prevent buff taking, or stop the enemy in a transit to prevent back-door uncapping. This gives less points than capping and defending, but it's a very important job on which my teams count on to control the middle buff and the "jungle".

you should not worry about points, just winning. I personally give up on some points by helping uncap and leaving my friend to the final capping while I go back to middle control

I wouldn't worry too much about points, since it doesn't give credit to really important things like stalling the enemy team, and someone who caps then immediately dies and loses a point repeatedly may not accomplish anything but padding their score. It's mostly there so people who are totally new to Dominion don't assume that kills and creep score are the most important elements of the map.

Ah well thanks then.