% Chance to increase potential tier?

I highly doubt the percentage changed. Do we have anything pointing at it? Your tiny sample alone is not really conclusive.

Why wouldn't Nexon change it? They never told us any numbers, and seeing as they are not exactly big on ethics they should have no qualms about reducing it. Then they can introduce new types of cubes and truthfully say the new types have higher success rates than regular cubes, when in fact they could be just the same rates as what regular cubes originally had.