TEST #1
Bull's Eye
Skill at lv11 : The target's defense to ranged attack is reduced by 60% during 20 seconds. (it works for party members.)
Related stats
physical dmg :
1000 - 1000
weapons : lv40 A Nelvin Long Bow (Life) & Nelvin Quiver (Life)
Situation
Dungeon: lv49 West Abyss
Test: 2 identic mobs, one was given the Bull's Eye debuff (maked by the red triangle dots and a red circle), and charge shot was used on both at the same time.
Observation
These 2 hits are both called ordinary hits because they are not critical. The target's defense affect the dmg that your skill can do with an ordinary hit.
Charge shot did 5283 dmg on the mob debuffed while did 3588 dmg on the one non debuffed.
In this case (for non critical hits only), the dmg of charge shot can be increased by about 47%.
Conclusion
Bull's Eye at lv50 can enhence the dmg of non critical hits immensely (by about 50% in tested case) on a particular target.
Supplemented screen shots

no.1 Under the same conditions, when charge shot crits, it always does 8022 dmg on these mobs.

no.2 Under the same conditions, when charge shot does non critical hits, it always does 3588 dmg on these mobs.