Many agree position #1 performs the highest as far as CTR and Total Conversions. But this is disregarding Cost per Conversion (and to an extent, conversion percentage rate).
If say you have three competitors bidding on the same keyword (let's also assume Quality Score is the SAME for you and your competitors)
Competitor A Bid - $2.00
Competitor B Bid - $1.75
Competitor C Bid - $0.75
It is widely accepted that your conversion percentage rate is the lease effected by your ad position - it is mainly dependent on how well your ad is targeted and your 'offer'.
But in this case, which is probably not that uncommon, the cost per conversion is going to be much lower if you bid $0.80 instead of $2.10. Yes, you will probably get less conversions, but the savings in the lower cost/conversion could be re-allocated elsewhere for better ROI.
It seems to me there is a high chance in many cases you have more than one competitor that is striving to be #1. In fact it probably isn't uncommon for their to be an almost constant stream (in higher volume keyword categories) of relatively new competitors to the Adwords market that come in with less knowledge and go for #1 at almost any cost before learning their lessons.
With the bidders in the auction potentially changing or changing their bids as time goes on, you really can't rely on the bids to be stable for any length of time. This would tell me trying to look a small period over time with different average ad positions (by altering your bids during those periods) wouldn't be a very reliable way to find the gap. Sometimes it might work when there are few and consistent competitors I suppose.