> your site will be a bigger determiner of CR than your position (for the same ad).
True, more precisely the landing page, not the site. But the LP was the same. So obviously, all being equal (landing page and ad, which is what my last compilation was), the positioning has some sort of effect. As I said earlier, those at the top have first crack at making the sale and will convert more often.
You're right of course that it's not CR alone, ROI as well has to be taken into account. But CPC doesn't vary as much as most think across positions, at least not in my data. And since CTR grows more exponentially than the CPC, the few extra cents for the few extra percentage in CTR is worth it, even more so if CR is stable across positions, a lot more so if as I believe the CR is higher in upper positions. In other words, my conclusion is that you want to be at the top to maximize revenues and profits.