The way I see it, the mana vision skill is the minimum skill required to solve the puzzles, actually solving the puzzle is basically a 'can you pay attention at all?' test, this is just to eliminate those who don't even pass the the most basic of requirements after all, the real test is later if I didn't read thing wrong.
so, solving more puzzles is basically a test of how commited you are, probably closer to a personality test and random skill checks than anything else, since you get the test number after a single puzzle people can just ignore the rest if they don't have patience