The way the Sizmek calculates sizes is definitely out there. Your zip that you upload is different from their "Workspace". They don't count everything in your zip. As I understand from their guidelines, after you upload your zip to the "Workspace", each element is automatically compressed on it's own and then recalulated. (Only the largest video is counted if more than one video. See second link for other "exceptions".) Odd and overly complicated, I know. One of the several reasons I steer clients away from Sizmek. Every time I work with them, they dodge questions or simply won't answer and arguments all the way. Emphasis added is mine.
~under Rules and Guidelines @ https://support.sizmek.com/hc/en-us/articles/200722459--overview-HTML5-Workspaces
"Ads that contain additional assets are calculated exactly as ads with Workspaces only; however, there is one exception. If the ad has an additional asset that is larger than the largest video in the Workspace, that asset is included in the calculation instead of the largest video.
The following table describes how ad size is calculated according to the different ad types..."