I read the adsense rules and FAQ's and it states I can't have an ad unit above the fold that takes up a large portion of the users screen and they specifically mention the 300x250 ad unit.
I used the 320x100 ad unit above the fold for a couple of days and made no money off it, however the 300x250 unit placed below the fold scored me more than $0 RPM.
So my question then is, am I no longer allowed to have an ad unit on my mobile site that is above the fold? If this is still allowed, then why am I making $0 even though I'm using an ad unit that doesn't take up the majority of mobile screens?
Is there a set of rules google is keeping away from publishers that we publishers should know about with respect to placing ads on mobile sites?