Concentration

[redpaint]

The skill concentration: it says it allows 2 mana regen (with more at higher ranks of the skill) every turn in combat. But I've realized that this is not entirely true.

For the first 9 rounds of combat I get +2, then at 10 rounds through 19 rounds it's +1. Then after 20 I get zero. Is this the way it is supposed to work? And if so then does this mean that at higher ranks of the skill the same 50% reduction every 10 rounds rule will apply?

Is there anything else that works like this on a 10 round basis?