For instance PHP setting 10 MB means that you can set the max size in Chevereto to anything like 2MB, 5MB, but not 11MB. You can't override server max limit, is really simple. Arvixe limit is 512 MB which means that you can use 2, 4, 15, 512 etc.
Like I've told you several times before, the max image upload size limit depends on the server setting to set the max allowed limit. The limit used in Chevereto is the limit that you set in your chevereto installation, not the server max.