I have a 4x enchant defender runestaff that also enhances dexterity by 11 (+5 bonus in my case). What's the best way to measure the defender bonus?

Using reflected casts of spell 111, I measured the difference between my DS in offensive stance with the defender runestaff and another regular 4x runestaff. My DS was 12 higher with the defender runestaff. Is that a good way to test it? Is the dexterity enhancement interfering with the test? I though defender bonuses were usually around 4 DS or so.