To keep sections from splitting into separate HTML files even when there is body content between headings that are assigned the Split property, you have two choices:
Prevent the content from affecting the split
Use alternative heading formats.
Prevent the content from affecting the split
To prevent a paragraph format (for example, ThinLine) that occurs between headings from interfering with keeping the headings together when SmartSplit=Yes:
[HTMLParaStyles] ; NoSplit prevents the para format from interfering with SmartSplit ; when it occurs between heads that would otherwise be kept together. ThinLine = NoSplit
Use alternative heading formats
For the affected headings, consider using alternate paragraph formats with the same properties. For example, you could define a paragraph format named Heading1x and use that format instead of Heading1 wherever you want to prevent a Heading1 split.