Reducing CPC with QS 10

Hi guys,

I have a legacy campaign targeting android devices that is having a good performance. One of my top keywords, have a 10 QS, ad relevance average, CTR 20% above average. No competition or very low in my niche.

I started this keyword with a CPC MAX of 0.40, the first days my CPC was 0.15 - 0.10, actually, after 30.000 IMP, the CPC is 0.06 and established. The avg of clicks per day is 600 with a 28% of conversion rate.

I would like to reduce more my CPC, the estimated top page bid is ?0.03, so I think that I can reduce my actual CPC an other 50%.

In order to do that I started reducing my CPC MAX to 0.17 and automatically adwords showed me this warning:


I checked with ad Preview and the keyword didn't showed ads. BTW, After three days with this warning my CPC have reduced to 0.04 - 0.05 and I'm getting clicks and IMP like before.

My question is: why I'm getting this warning if my ads are shown? Why ad preview doesn't show ads to me but yes to the users?

If I have no competition is a good idea to reduce the cpc max in order to reduce the cpc? Why adwords don't bid the minium estimated top page bid?

How Google calculate the CPC is there aren't other advertises?
Actual CPC = (AdRank to hit?/Quality Score of Advertiser) + $.01

There are a lot of questions, thank you in advance.

This also happens with many times as I also advertise only on the mobile platform. I have good quality scores and I am getting a good CTR but when I try to lower the bid sometimes it starts saying that my ad is not being shown due to low ad rank and still I am getting impressions and ads.
So far what I have concluded is that google's calculations are not accurate at all and they just aim at raising the cpc by showing such messages. But as long as I am getting clicks and returns I dont mind much.