Why doesn't the Water Dragon buff scale linearly, like the other three?

Is it intended that the Water dragon bonus doesn't scale linearly, but the other three do?

Look at restoration over 36 seconds with 18/12/6 second cooldowns:

1 stack: 2 restores 2 stacks: 3 restores 3 stacks: 6 restores

Linear scaling would be 18/9/6 second cooldowns. Over 36 seconds, that would result in:

1 stack: 2 restores 2 stacks: 4 restores 3 stacks: 6 restores

If that's just a case of poor math, I sympathize. Division is weird. The numbers were provided as inverses. And the inverses decreased linearly! But.. That doesn't mean the actual value they're describing grows linearly too.

I really can't imagine it was intended for the second buff to be such a small boost to the first, and the third was intended to be such a huge increase over the second.