HOWEVER, as you also noted, it does get read by the judges so that the emotions, setting, motives, etc., don't just appear out of left field.
But this is where it gets tricky. Because those parts aren't judged, I'm not actually sure whether or not you'd get a -10 deduction for going over. On the one hand, deductions only apply to judged posts and so it seems like you shouldn't, but on the other hand, as a judge, I'd be super annoyed if you wrote a 2000 post novel that I had to read (even skim) through.
All that being said, because all the other 'intro 0/3' posts have always had to be under 800, I would say that for continuity, yes, you have to keep it under 800.
If you want to write a huge intro and it's 0/3, then write it outside of the battleboards and take all the words you want.
:3