Too many authors think as book designers instead of as readers. Anyone who consumes many ebooks is quite used to these breaks, and likely be more annoyed at a likely outcome such as having a couple lines at the top of the "page" because the author put in a page break before the sub-head.
If it really bothers you, better I think just to get rid of the sub-heads.
When it comes time for the print edition, sure, deploy your design talents to get rid of the breakhead toward the bottom of the printed page followed by one line of type.
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