recasting

So supposedly for : NI it is 1 second for every 2% haste you have equipped. And : Ichi 3 seconds for every 10%. Now when i equip 10% haste, it knocks 5 seconds off : NI, but when i equip my 20%, it only knocks off 9 seconds. (6 for : Ichi though) My question is... if I only had 19 % haste or...