How to format header in `tufte-book`?

Question

I'm putting together a tufte-book whose page size is 5.5'' * 8.5''. I have most of the geometry worked out, but the page headers aren't cooperating. So I have this stuff in my preamble:

\documentclass[symmetric]{tufte-book}
\usepackage[oldstyle]{libertine}
\usepackage{verse}
\usepackage{geometry}

\geometry{paperwidth=5.5in,paperheight=8.5in,width=4in,textwidth=3in,textheight=6in,top=1in,left=1in,right=1.5in}

Which produces an OK text block, but headers cut off by the edge of the page (see screenshot). What's the remedy?

Update

Verso pages now look OK; on recto pages the header is still truncated.

Answer 1

Turns out the answer was to play around with marginparwidth and marginparsep in the geometry parameters. The magic numbers, for posterity, were:

\geometry{paperwidth=5.5in,paperheight=8.5in,textwidth=4.5in,textheight=6in,marginparwidth=2cm,marginparsep=2mm,top=1in,left=0.75in,right=1.5in}