Formatting chapter/title pages with offset blocks of text

I know there are some strong feelings out there about trying to simulate paperbook layouts in the context of reflowable, re-sizeable ebooks. For example, I've seen repeated calls against top margins on chapter headings or simulating text that starts "half-way" down the page, presumably because screen sizes and text sizes could potentially result in blank pages, unusual gaps between text, etc.

However...

I'm wondering how the pros here handle content that is seemingly necessary to format with various top & bottom margins and variable font sizes (see attached image). Do you assume a certain font-size (i.e. assume 1em is the size of some referent physical book, or assume a certain number of lines of text per ereader page) and screen size and hope for the best? What are these assumptions?

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