[Ascension] [Adventurers] Magicians

My apologies for a potentially stupid question, but I'm trying to understand Arcane Aim with Ascension hitting GMS next week.

I'll just use max level figures for the questions.

First off, the 20% Ignore Enemy Def - is that WHENEVER attacking a monster, or only after landing 3+ successive hits? Also, is this essentially useless for Magicians since it's Def, or does "Def" in this case refer to both physical and magical defense?

More importantly, the damage stacking - how exactly does that work? There's a 50% chance that after 3 hits my damage will increase by 8%? As in hits 4+ each carry a 50% chance of increasing damage by 8%, with a stack factor of 5? Meaning I'll be doing an extra 40% damage on the 9+ successive hits provided (1) they're successive, and (2) the 50% worked successfully each time?

Thanks for the help!

The def ignore is a passive boost that always applies.
The def ignore works for magic def too
Yes, after you stack arcane aim's effect 5 times, all damage on the mob will be +40%, until a different mob is attacked, or the skill is dispelled.