iPad 3 and iPad mini storage disparity

I have an iPad 3 and an iPad mini which i use to carry identical information. I noticed that despite selecting the same photo folders on in iTunes, after syncing the iPad3 had used up more than double the space the iPad mini had used for the same number of photos. Looking into this further, I found a number of smaller discrepancies with the number of items synced to each device when the selected sync data was exactly the same, such as slightly different numbers of song and videos that were sucessfully synced to each. However, my main concern is the photos, which are now taking up 22.9 GB of the iPad 3 storage as opposed to the 10.8 GB taken to store the same photos on my iPad mini.

As both devices were intended to store exactly the same info, I decided to restore the iPad3 from a backup of the iPad mini. Surprise surprise, the iPad3 still allocated 22.9GB for photo storage. Can anybody please explain the disparity in the space used and whether there are any published differences between the iPad 3 and mini which may account for this and the other discrepancies between the two devices after syncing?

When I restored the iPad 3 with the mini's backup I didn't factory reset the iPad 3 first. Could this have affected the storage allocation?

All syncing, restoring and backup was done using a USB cable to a Windows 7 PC running iTunes for both devices.