The top positions that you reference are generally reserved for our Premium Sponsors. AdWords ads may appear in these positions on ocassion. This is an additional bonus provided to those advertisers with ads that meet google ad position criteria. Top placement is determined by an ad's clickthrough rate (CTR) multiplied by the maximum cost-per-click (CPC). The ad rank formula gives advertisers an equal and fair opportunity to attain their desired ad positions and offers greater relevancy for Google users.
In the end if the keywords are in the title (and hence bold) that is 99% of the battle.
In my experience being top is normally a function of $. You just need to slap it on the table.
Of course, once you are top you also get better CPC. I don't know if Adrank weights your CPC by your average position, but if it doesn't then the algorithm is flawed since obviously higher ads get higher CPC regardless of the ad copy.