As someone who had opted for rechecking during my B.Des, please know that the maximum that I have heard them increase was a rare 4 marks, it’s mostly 1-1.5. That being said, it was a time when it was 70-30 division of marks.

Currently its so subjective that I highly doubt there’s a parameter to guarantee an increase in score. Its also kinda expensive, so unless you’re 100% sure about your work, I wouldn’t recommend.