I haven't really looked in depth at how the lightning staff does damage but with the change to when the lightning staff does the AoE ticks I recently had a close look at this.

1. Both characters have ONLY 2 points into Tri Focus in the Destruction Staff Skill Line (no other skills, no CP, no gear)
2. Thus, the Tooltip reads "Fully-charged Shock Heavy Attacks damage nearby enemies for 100% of the damage done."
3. The lightning staff hits 4 times per channel, 3 ticks called Heavy Attacks and a final Shock Pulse which is 1.4 times the Heavy Attack.
4. In both cases I attacked two hoarvors.

On Live

Main Target:Nearby Target
531:404
531:404
531:404
745:566


On PTS

Main Target:Nearby Target
692:0
692:0
692:0
968:794

5. At no point on Live or PTS does the splash damage on the Nearby Target do 100% of the damage done to the Main Target.
6. On Live the hit to the Nearby Target is 76% of the damage done to the Main Target.
7. On the PTS the hit to the Nearby Target is 82% of the damage done to the Main Target.

Question: Why isn't the damage to the Nearby Target 100% or the same as the damage done to the Main target?

8. Live: Main Target to Nearby Target Damage = 1.3:1
9. PTS: Main Target to Nearby Target Damage = 3.8:1

Question: Why is the Nearby Target Damage on the PTS only calculated from the final hit on the Main Target and not all 4 hits?

Suggestion:
I understand that the Lightning Staff was never meant to apply any bonuses to the first 3 hits of the channel (whether they are set bonus/skill bonus/splash dmg), however the current change completely alters the function of the Lightning Staff.

Please update the tooltip to reflect the actual damage the nearby target(s) will receive to reduce confusion.

In order to maintain the function/role of the Lightning Staff (which is based on the splash damage to nearby targets) adjust the final hit from the Lightning Staff to do Y% of the total damage done by the Lightning Staff attack channel. This would alter the above PTS Nearby Target damage so that the hit would be 2496 or 82% of the total damage done to the Main Target.

This isn't as ideal/functional as the current splash with every hit because if the target dies before the Shock Pulse at the end of the channel, no splash damage will be done at all.

Personally, I would be happiest with the Live damage pattern BUT with the 3 ticks NOT proc'ing bonuses that require a fully-charged heavy attack!