Class Rank points are referred to as Skill to help with the confusion. Physical Level is Exp.
You get Skill points depending on your Class Rank vs. the level of the mob. If your Class Rank is too high compared to the mob you will receive very little skill, sometimes none.
You get EXP points depending on your Physical Level vs. the level of the mob. If your Physical level is too high compared to the mob you will receive very little EXP, sometimes none.
From what I've seen, you will stop gaining Skill from low level mobs before you will stop receiving EXP.
If this is not completely correct, anyone, please point out what I'm missing.