Do Split Gallows have rules?

[pfeaster]

Paragraph initial words primarily, but not always, begin with a plain gallows (K, F, T, P) and almost never a benched gallows - but…
When a paragraph does start with a benched gallows it is most often going to be a split gallows.

There certainly appears to be a pattern, whether or not it rises to the level of a set of "rules" or not.

I wonder whether this pattern might be due to the same factor (whatever it is) that discourages benched gallows from line-initial position generally. That is, could whatever discourages benched gallows from appearing at the start of "ordinary" lines also have a tendency to produce split benched gallows at the start of paragraph-initial lines?  Could these two patterns together reveal something about the logic behind how gallows and benches interact?