The IPs are supposed to grade you according to the course training standards listed in the syllabus. Unfortunately, the grades they give you aren't as black and white as what the syllabus states so they end up being pretty subjective. Check out the T-6 syllabus and it should give you an idea of what they're looking for (start at page 13).
https://www.t6driver.com/jsupt/jppt_jsupt_syllabus.pdf