Alchemy potions not increasing in value?

Malufus

The short duration potions like "increase spell crit" and "detect hidden" and....well basically all the non heal/stam/magic replenish potions do NOT increase in any values(duration/effect amount) by using higher tier water

is this intentional or a bug?

Merlinus

i heard the it increase by % so you don't really notice increases in duration of invso,ect till higher lvl