How does Devouring Arrow work?

While trying to figure out the math for Hungering Arrow, we discovered that we don't know how the Devouring Arrow rune works:

Hungering Arrow: Fire a magically imbued arrow that seeks out targets for 115% weapon damage and has a 35% chance to pierce through targets.

Devouring Arrow: Each consecutive pierce increases the damage of the arrow by 70%.

Does this mean that each hit gets another 70% weapon damage added (so a second hit would be 115 + 70 = 185%)? Or that the total damage is increased by 70% (so a second hit would be 115% * 1.70 = 195%)? Or something else? This doesn't make a big difference on the first hit but the cumulative effect could be large.

Solution 1:

I tested it and it is most likely that it is the 185% so it just adds 70% (115+70)

to the data:

normal hits without pierce made up 50 dmg that are 115%. so 100% wpn dmg was about 43.47 i'll take 44. 70% from 44 are 30.8. so one pierce would make 80 dmg, 2 would make about 110 dmg and 3 would make about 140 dmg

I shurely collected more data. one Pierce made about 80 dmg 2 pierces made about 110-120 dmg and 3 pierces made about 140-155 dmg

As you see it is the 185% weapon dmg.

All data was made with a 16.5 dps 2 handed crossbow 14-16 dmg without any other gear on a mallet lord in act4 hell with my DH lvl 60. Additionaly i had no dmg buff passives active (had hot pursuit, brooding and tactical advantage)