AdSense mystery

So I'm having an AdSense mystery with my work sites and I wanted a large space to lay it all out and hopefully get some ideas/pointers on what I'm doing wrong from anyone in the AdSense community.

We have a site for our industry publication, QSR magazine with a mobile version/theme. The first half of this year, I simply had an AdSense spot at the top of our page and it was clipping right along with pretty decent AdSense revenue. In trying to quantify that, I'm confused with AdSense reports with two different products: AdSense for Content and AdSense for Mobile Content. If I just look at July, though, I just see AdSense for Content for our mobile site, so let's just isolate that:

• 39,426 page views, 162 clicks, $120.47 earned

Ok, so my bright idea was: Hey, this is based on one banner ad. What if we update our mobile site to have 4 leaderboards on each page? We could multiple our revenue! I also wanted to consolidate our banner management with our other system (DFP), so I updated our site templates to use the new DFP ad code and created the 4 slots in DFP. This would also allow our advertisers to advertise directly on our mobile site, too.

But what I'm seeing is a dramatic reduction in CPC. We have yet to have direct advertisers, so all impressions are being delivered through AdSense in DoubleClick, but the (revenue) numbers aren't what I was hoping. We made the switch on August 31st, so if I compared November to those July #'s, here's what I'm seeing:

• Mobile Leaderboard #1: 25,794 impressions, 122 clicks, $20.37 earned
• Mobile Leaderboard #2: 24,826 impressiosn, 92 clicks, $11.22 earned
• Mobile Leaderboard #3: 20,714 impressions, 56 clicks, $4.37 earned
• Mobile Leaderboard #4: 22,671 impressions, 9 clicks, $0.58 earned

So my question is why am I seeing such a huge reduction when using DFP vs. AdSense directly?