eCPM is a estimator, it just give you some idea how much you going to earn with your current status. To increase the eCPM, you need to improve on your CPC and CTR
I would not worry about your ecpm, concentrate on the type of content you create and the traffic you get.
Yes, as i mentioned that is just estimator, it depend on your CTR and CPC. Higher CTR and CPC will give you high eCPM