Rates for film sound design?

[citysoundman]

Hi Everyone,

I may be working as a sound designer on a narrative film. Most of my work is post mixing/editing with sound design work as needed, and I will usually work out a day rate for all of these services put together. But I believe sound design rates for film are not set by the day. I'm hoping to find out how rates are usually set for sound design work for film. I'm talking about indy films, not big budgets. Is it true that many people charge by the real-time minute of picture? Can anyone give me ideas of rates for both feature-length films as well as shorts?

Thanks in advance!
Bob