At the difficulty im playing at, I summoned a skeleton guardian and it took 21 flash bolts to kill it,
so it had about 420 health.

my bow and arrow does 20 damage per hit, and is enchanted with weakness to magic 100% for 6 seconds
I shot the thing 5 times, meaning my firespell should be 2,4,8,16,32 times more effective
So the final fireball after this should obliterate it.
But it didnt, it needed to.

Testing how many times i needed to shoot it for a one shot to occur with my flash bolt spell, the result was 7.
I needed to stack weakness to magic 100% 7 times to do 300 damage with a 20point spell
Why is this? I should just need to apply it 4 times to get to the 16x magnification i should need to kill the skeleton with one shot.

Whats going on??