Between partially and largely

I want to say that

This chapter is based partially on [a paper I coauthored]

but "partially" doesn’t feel right because the overlap is maybe 60%.
But

This chapter is based largely on [a paper I coauthored]

seems to suggest more overlap than actually occurs.
I feel a need for a word conveying
substantive overlap, but neither partially nor largely.
"Substantively" doesn’t sound right to me.