Handbrake and 16:9 movies

Hey all,

I'm running into a bit of a conundrum, and I was wondering if anyone could help.

I have a movie in a .mkv container (1080p, the whole shibaz), that i'm trying to convert for my iPhone 5. I've converted it before, using the standard iPhone preset, but I've realized that if I can convert it to 16:9 .mp4, it would look perfect on the screen.
The problem is.. I don't know which settings to tweak to make it into 16:9. If anyone can provide me a walkthrough or send me in the right way, that'd be great!

Thanks!