FixedHeader with responsive Bootstrap 2.1

I'm using FixedHeader with a Bootstrap 2.1 responsive layout which has a fixed navbar when the window width is >= 979px, but un-fixes itself and scrolls off the top of the page when the window shrinks to anything less. This, of course, causes my fixed table header to be set 40px too low when that happens.

Can anyone think of a way to reset the offsetTop to 0 when the window shrinks to less than 979px?

Thanks!