How do I resize the footnote box?

I'm using footnotes in my dissertation (and using Pages because it's the only way I can use multiple images and stay sane). But the footnote box is bizarrely wide – as wide as the footer, rather than matching the width of the text, as required by my printing guidelines. If I increase the right margin, the main text becomes stupidly narrow. I can't see a way to resize the box that contains footnotes, or (even better) make it match the main text frame.

Any ideas?