Getting the top position on Adwords

As far as I know, the position of your ad is determined by the click-thru rate, and not by how much you pay for the phrase. Correct me if I'm wrong about that.

So, assuming that's still the case, how can your ad immediately grab the top spot as soon as you make a campaign live?

Does Google take the ad's CTR history into consideration. An ad I'm running did have several top spots but the ad was paused for a fortnight. Now I've activated it again, and it's got the top spot already.

I'm not complaining, of course I just want to understand why it's getting the top spot.

Congrats on the top spot!

The position depends on the CTR and your MaxCPC. Newly started campaigns get "seeded" with a factor to help them get exposure to see if they accumulate a CTR. As the number of impressions increase, the factor diminishes until eventually the listing is depending on it's own performance.

Your campaign had already accumulated its own CTR (it doesn't get reset just because you pause the ad) and your MaxCPC is evidently still high enough that, combined with your CTR, it warrants the number one position.