Sudden jump in Adsense CPC

Hi guys,

Let me tell my history with adsense. So I have been using Adsense since 3 years ago where I first started off with my main site. Let's call this site main.com. It was a general tech blog site which is totally white hat and I slowly built it up for about 1.5 years where it was averaging 900-1000 unique visitors a day. I noticed the more traffic I got, the higher the CPC which could be attributed to the CPM as well as ppl probably bidding for a placement. I was getting around $0.50 per click on average which I think is pretty good. Sometimes I could even get $1.00 per click. So that was all good till Panda hit and my traffic tanked to about 100 a day. Now it's only about 40 users a day. After that most of my CPC was averaging about $0.15 per click.

So I gave up on the site totally but I left it still up and running and started 2 other niche sites which has its own domain but sitting on the same server. I took my time to slowly built up the 2 sites and let's call first niche site niche1.com. So niche1.com gained decent traffic with all white hat techniques which grew gradually from 20 UV to about 300 UV per day over a 1 year period. I put more effort on niche1.com with about 50 articles and less effort for my niche2.com which has about 30 articles. So over that 1 year period all 3 sites has been consistently getting $0.15 per click until a few days back. My niche1.com is actually a quality site with low bounce rate and long visit duration and google was sending quite a bit of traffic to it in the past month.

The strange thing is my niche2.com got a $1.00 CPC a few days back main.com managed a $0.80 CPC and now all 3 sites seem to be getting very high CPC. So my question is does adsense put a cap for all your sites if they find that one of it is converting poorly which could be from main.com since it's a general site? It seems like niche1.com managed to convince them to lift up the cap if any.