I think each level test is designed based on the current situation of the participants.
Like in case of Headon, normally people enter the tower one by one, thus they will have to be tested one by one as well. The test with that big fish fits that category. The same goes with the level test which requires help from other positions as well. The grading is for all of them as a group and as an individual, of course the test would be made more difficult.
I am confident that we will see more level tests, after all we're going to see Baam fighting his way once again to get to where Rachel is. T__T Perhaps not now, as the attention of the chapter shifted from Baam to the Zahard prince, but we will see it again. ^^
Well, I understand with Headon's test because he has to weed out the Worthy, The Non-Worthy, and the Irregulars by giving them the test. The 2F's Guardian test is what confuses me. If Baam and Rachel wouldn't have gotten any help from the other Regulars would they have failed the test in the end? That's what I am trying to figure out.