From what I understand, Google can position your ad above the ad of others who are bidding more than you if you have a superior Quality Score. Thus my question....
If the system raises the bid when the ad is already in the top spot (especially if it is a high volume keyword), then the system needs to be adjusted or the keyword needs to be managed manually.
There are the ROI calculations that lots of bid management systems work off of to determine what the bid should be and then there is the reality of the bid marketplace. Those bid management ROI calculations for setting bids worked better in the Overture model than today's bid environment.
When an ad has a high CTR and ranks near the top, one way I found to make a lot more money from it is to drop the bid to #0.01 below the actual current CPC for that keyword. This may or may not cause the ad to drop in the rankings (it probably will drop a little bit in most cases) but the average CPC can drop dramatically while volume stays almost unchanged and profits go up.
If the system raises the bid when the ad is already in the top spot (especially if it is a high volume keyword), then the system needs to be adjusted or the keyword needs to be managed manually.
So raising your bid if you are already in first position, does not raise your cost since, assuming all else remaining equal (which it never does by the way), your cost will be the same.
you cannot say to do one thing and expect a certain result every time
If you are not in first position, raising your bid raises your positioning but now you have changed the parameters. The ad below you is probably not the same and therefore the cost will be different. It may go up or down or stay the same.