Here are some quick, non-mathematical thoughts regarding your bidding strategy.
There is a fair amount of research that indicated that, in general, the higher your ad ranking on a search engine results page, the higher your conversion rate. So there’s one strategy – bid to get to the top. The problem, of course, is that you can end up in bidding wars which drive your bid prices way too high. Even if that does not happen, you could still end up damaging your return on ad spend by paying too much. It is a balancing act between paying a price that generates a reasonable ROAS and that generates enough conversions to make it worth doing to start with.
There is also evidence that in some circumstances, especially with lower volume “long-tail” keywords, LOWER ad positions generate a higher conversion rate. So applying this to your overall strategy, you want to bid for higher rankings on your high volume, general purpose keywords and low for your low volume, more specific keywords.
Ultimately (as we have said many times), user behavior is completely unpredictable, so you won’t know what works until you test different strategies and see.