Why Lower Ads Often have Better ROI:

The lower ads have a lower bid price. That can help save money if the top placed
ads are overpriced. Another great benefit of having a lower ad is that a user that
clicks on one is more prequalified to make a purchase. By scrolling through a bunch
of ads they have displayed a greater intent to make a purchase.

These two mathematical facts often mean that listing at 5 or 6 often provides a
better ROI than listing at the top. You will need to determine the profit elasticity
for your market to see what ad locations will return the highest overall profits.

Lowering Click Price after Bidding:

After you get 10 or 20 clicks and have a decent click through rate you may want to
slash your bids in half or by 2/3. Often it is best to start off with your ad around
the #1 or #2 positions to collect feedback and then let it fall back after you drop
ad price.