Yes, that may be true, However, keep in mind that if it is true for you it must also be true for your competitors. PPC is auction-based, so your competitors are likely making a profit at whatever the ad positions cost, else they would bid that high, right?
You need to equal, or best, your competitor’s profit from the gross margin, multiplied by conversion rate, else you will get squeezed out of the market. Any improvements you make on conversion rate will make up for differences in gross margins. The focus in improving conversion rates, as well as gross margins, and Quality scores.
