I read the following policy on google:
Is placing a 300x250 ad on the first view screen of a smartphone considered a policy violation?
Yes, this would be considered a policy violation as it falls under our ad placement policies for site layout that pushes content below the fold. This implementation would take up too much space with ads on a mobile optimized site's first view screen and provide a poor experience to users. Always try to think of the user experience on your site — this will help ensure that your users continue to visit.
As long as the main content stays above the fold and doesn't affect the user experience, you could consider implementing a 320x100 as an alternative.
I then decided to place just one 320x100px ad unit centered and at the top of the image page. and for the past few months, I've been consistently making $0 RPM. Now I'm beginning to wonder if a CDN is mandatory for me because when I ran tests on the site, testing it on a machine close to the server shows an < 10ms TTFB (time to first byte) where as testing it on a mobile device from western USA (where I think google is) shows about a 320ms TTFB, however when I tested it from a desktop computer in the same area in USA, the TTFB is under 200ms (which is what google recommends). On my desktop site I'm making something in RPM, but never on mobile site.
Here's a screen shot of a recent test for the mobile site:
And also, if I use a CDN, what limitations do I have with regards to updating my site (for example: how long will it take before users see updates)? (Sorry I'm new to CDN's but if it helps me solve my issue, I'll consider it)
Sometimes the site is updated a few times a day, but when things go haywire, I sometimes update it like once every few seconds to make sure problems are fixed.