the cooldown isnt the same as the spell lasts, the cooldown is almost twice than thatI could be mistaken but rapids cool down is always the same as how long the spell lasts.
You should probably read the post from the beginning criminal as both Ailwen and I keep rapid at 1/35
and also, if the cooldown wont change by lvl, then at lvl 20 the skill will last for 15-16 secs while the cooldown is 10-11 secs, u can cast it over and over again
So I tested rapid with 1/35 , 5/35 , 13/35 , when cast rapid duration lasts exact same amount of time as the cool down .
I'm not sure where you got those numbers from dude.