Not really sure how else to say this, but the default comment box height is HUGE and takes up a buttload of room even when there are zero comments. You can see a live example here.
It seems to take up 90% of the viewport for some reason?
It's inheriting that style from your blog - you can change your CSS to fix it. Let us know if you need help with that.
I'm confused where its pulling it from sorry, I see .Stream__tabContainer___2GahZ setting min-height: 600px?
No problem! The div id is "talk-embed-stream-container"