My opinion would be if you change the quantity you would not be comparing the flavors at different times of addition but comparing different quantities at different times of addition. 2 different exbeeriments. 1 comparing flavor alone and 1 comparing flavor at a set bitterness. For example it would take 5.5 oz of cascade hops to bitter a 1.044 gravity beer to 30 IBU at 5 minutes. Not something you would normally do. But to compare what an oz of cascade added at different times would give you useful info.