Auto scrolling is done by the Scintilla editing component Geany uses. It has a number of policies [available](https://www.scintilla.org/ScintillaDoc.html#ScrollingAndAutomaticScrolling) and currently Geany sets `CARET_JUMPS` and `CARET_EVEN` for x policy.
It would probably be reasonable for someone to provide a pull request that makes some/all settings available via a user setting, probably in Preferences->Editor->Display, next to `Lines visible around the cursor`.