Darkness

Never done much research with darkness but I would like to understand it better;
I've noticed on low humour characters I have in very shallow darkness, their soft humour drains. (The first part out of Soft/Hard/Max humour numbers, as you see in enders client.) But, when I go deeper with my fighter, eventually his hard humour starts to drain, instead of the soft humour. (The soft humour just goes down because the hard is.) One thing though, even though they're off balance by about 20, they start draining at the same time when hard humours start to drain. I assume there is two darknesses?: At first it only drains your soft humours if they're below a certain threshold, but at a certain point it switches to hard humours.
Could someone explain this to me or confirm my hypothesis?
I've noticed on low humour characters I have in very shallow darkness, their soft humour drains. (The first part out of Soft/Hard/Max humour numbers, as you see in enders client.) But, when I go deeper with my fighter, eventually his hard humour starts to drain, instead of the soft humour. (The soft humour just goes down because the hard is.) One thing though, even though they're off balance by about 20, they start draining at the same time when hard humours start to drain. I assume there is two darknesses?: At first it only drains your soft humours if they're below a certain threshold, but at a certain point it switches to hard humours.
Could someone explain this to me or confirm my hypothesis?