Getting confused now!

Entrecard is getting so confusing to me now and I can't figure out if I am doing something wrong without knowing it or what is going on. I used to pay out big ec's for advert space. Then the 4096, 2048, 1024, 512, 256 prices started bringing in numbers anywhere between 2 to 66 ec's. Then I started trying to buy the cheaper ones and they are even worse. For 4, 8, 16, 32, 64 prices, I'm getting anything from 0 to 6 ec's. On "My Ads page" I saw 8 to 10 in a roll that paid back 0 ec's. What am I doing wrong???? Starting to get the idea it's not worth it anymore.
Then 3 days ago I see my recipe blog is up in the 8000 price area. Who in their right mind is going to pay that to place an advert on anyones blog? But then again, if people are getting back ec's like I am lately, then they can't have the kind of ec's it takes to pay those prices.