I would say the ad position has an impact on conversion, but not for all markets. If you need a fast service like locksmiths, help on-road and etc, yes. Users will take decisions really quick. If it's a house siding company, landscape design, furniture - user will go beyond the first page. But this user behavior tells that he considers far more offers than yours, so you better have a good deal to offer. I have campaigns, where my bids below the first page, but I still manage to keep ROAS at 3x. If a keyword doesn't have much volume, then you will get no enough data to optimize. I had this problem with a very specific niche. The bid were below first page and I received only a few clicks. So i HAD to bid more :)