The fact that a HR is not predetermined is a frequent trivia in this game. So I'm sure... At least in gameplay, it's not predetermined. It's physics based there (ball flight path, air condition, park dimension, etc.).
I know the sim engine is different from gameplay engine. From what I gather from a bunch of older Brian@SCEA posts that I've read recently, these two modes even get worked on by different engineers (Brian does the gameplay).
I think the sim engine is not as elaborate for sure... so I wouldn't be surprised park factor and such are not taken into account, although it could be done in theory...