Thanks to the ladder reroll, quite a few rumors have popped up regarding the function of Fortitude and Grief on Smite. I have already explained how it works with a normal attack, so now it is time to destroy the much more prevalent rumors regarding Smite.
Part I: Fortitude
There is a rumor flying around that ED% from outside the weapon doesn't affect Smite. This stems from the fact that no difference shows up on the damage screen when something like Fortitude is equipped on a Smite-based character. This turned out to be a fairly easy test to prove.
Since my V/T is built to use Enigma, he was unable to equip Fortitude. Because of this, I had to use my Zealot, Stoutwood for this test. Stout, with 1 hard point in Smite and a comparatively low level Fanaticism, required a +399 Grief to boost his damage so that a difference would be recognizable. I removed all items that could skew the results, such as items with Crushing Blow and Open Wounds. The-Professor was unavailable for this test, so I enlisted the aid of my friend Oakenshaft, or Mr. J as he is known on these forums.
Mr. J removed all +life replenish gear from his character, and also made sure to get 50% DR for the ease of calculations. I then proceeded to Smite him 5 times with the Fortitude equipped, and 5 times without. We subtracted his remaining life after getting Smited from his life beforehand to get the total damage applied.
Displayed Smite Damage: 1236-1314 (with a +399 Grief Phase Blade equipped)
Damage Done to Mr. J Without Fortitude:
Trial 1: 2006 - 1523 = 483 Damage
Trial 2: 2006 - 1521 = 485 Damage
Trial 3: 2006 - 1530 = 476 Damage
Trial 4: 2006 - 1530 = 476 Damage
Trial 5: 2006 - 1529 = 477 Damage
Damage Done to Mr. J With Fortitude:
Trial 1: 2006 - 1387 = 619 Damage
Trial 2: 2006 - 1389 = 617 Damage
Trial 3: 2006 - 1386 = 620 Damage
Trial 4: 2006 - 1387 = 619 Damage
Trial 5: 2006 - 1387 = 619 Damage
Conclusion: Obviously the 300% ED from Fortitude adds into the Damage equation, regardless of whether or not it appears on the character screen.
Part II: Grief
There are basically two theories as to how Grief works with Smite. Theory 1 states that the displayed damage goes through the PvP Penalties and Damage Reduction, and the +Damage from Grief is applied aftarwards straight up with no reduction. Theory 2 states that the +Damage from Grief is added to both the maximum and minimum damage of the shield, where it is then multiplied by ED from Strength, Smite, Fanaticism, and ED from non-weapon items.
This test was done in a similar manner to the Zealot Grief Test. All items that could skew results were removed. 5 Trials were performed with the Grief equipped. This part was done with my V/T, so the damage was equal to that put out by any other Smite-based build.
Displayed Damage: 2750-2793
Actual Damage Applied to Mr. J if Theory 1 holds: (((2750-2793)*(1/6 + 1/2)) + 398-398) = 627 - 630 Damage
Actual Damage Applied to Mr. J if Theory 2 holds : (((589-592)*(13.4+1))*(1/6 + 1/2) = 706 - 710 Damage
Trial 1: 2006 - 1283 = 723 Damage
Trial 2: 2006 - 1282 = 724 Damage
Trial 3: 2006 - 1284 = 722 Damage
Trial 4: 2006 - 1283 = 723 Damage
Trial 5: 2006 - 1284 = 722 Damage
The odd thing about this test was that while it was very close to the anticipated results of Theory 2, it was consistently above the maximum expected value. This worried me, so I did a control test without equipping the Grief. The displayed Damage was the same, so the actual damage applied to Mr. J would be 229-232.
Trial 1: 2006 - 1769 = 237 Damage
Trial 2: 2006 - 1769 = 237 Damage
Trial 3: 2006 - 1769 = 237 Damage
Trial 4: 2006 - 1771 = 235 Damage
Trial 5: 2006 - 1769 = 237 Damage
These results also came out consistently higher than the maximum expected value, so whatever the problem with the equation was, it wasn't the Grief. I quadruple-checked my V/T to see if any other items could have possibly boosted the damage, but I didn't find anything. I also went over Mr. J's gear. He was wearing a Stormshield, Ethereal Upgraded Shaftstop, and a 12% DR CoA.
This leaves two possibilities: Either Smite has an odd quirk that boosts it's damage slightly higher than the displayed value, or Ethereal Upgraded Shaftstop has a bug that prevents the 30% DR mod from functioning. This however, is a topic that should be dealt with in another thread. At any rate, it is reasonable to say that the +Damage modifier on Grief adds directly to the shield damage and is susceptible to PvP penalties and Damage Reduction.
EDIT: Further tests have shown that Ethereal Upgraded Shaftstop works fine. There has been the suggestion by several people that the offset is due to the PvP penalty being slightly lower than 1/6.