CPC decreased by 30% or so, so the eCPM increased only by something like 30%, though no clue as to why.
It's soon to say. Your design modification seems to be just one week old, according to Google's and MSN's caches (Oct. 18 or 19). I don't see any reason for a decrease in CPC in your design, which is not confusing at all. If I'm not wrong, quite possibly these are normal CPC variations, going a little up and down as always. So, you may wait another week or two. You can see what I mean by making graphical charts (of CPC, etc.), with your CSV file (downloading from Advanced Reports in the AdSense account). Perhaps you are doing it already, for example with Excel. There are other many possible tools for this, like the freeware CSV AdStats, etc.
Thanks bugon for this tip... i think it is all to make visitors see the ads... if they are on topic they will click on them