The edge→zone distance was document-wide, so an index whose header starts 4cm
down had its body open 14.5mm too high and the page under it followed. HfSet
carries the section's own pair (and its first page's, where the page style hands
over): ODF's page-layout margin is that distance, Word's is w:pgMar
w:header/w:footer, and both exports write it back.