Why can't I sync my purchased HD movie to my iphone 4s?

I have bought and downloaded an HD movie from the itunes store through my mac book pro. I have confirmed that my mac book pro is HDCP compatible and have completely downloaded all formats, HD SD & itunes extras. However, when I tried syncing it to my iphone 4s, it only loads the SD version. Why is this so? And how can I use the HD version instead of the SD version? This is disappointing since I paid for the HD price but am only getting SD content?!