This answer to a previous question on StackOverflow suggests the base used for the cherry-pick command is the parent of the commit to be cherry-picked. It makes a lot of sense to me, but I wanted to possibly verify it using the official documentation from git developers. Does anyone know where I can find the official documentation?
I do not think anything will beat code. Look around here (and the code before it inside do_pick_commit):
https://github.com/git/git/blob/master/sequencer.c#L2182-L2225