@aury88 I can check for you if there is a file size etc but none has been mentioned so go with the other criteria for now. As for the clock and circle and having just looked at my nexus and OPO, I would say its a matter of not having all the important or small detail where they fall and so get obscured. Especially with the circle stats around it.
The screen sizes across the devices vary that much (BQ 4.4 to M10) you can't do much else. The circle is 4cm on the bq and 4.3 0n OPO. So just keep it in mind. You don't want your best efforts hidden away.
I or some one else will get back about file size.
edit just a quick thought can you find the existing wallpapers using file manager and get any info that way. Haven't tried myself I must admit.