Did this on an Arboreal Bastion in Yorcia Weald using Aero in various combinations of Dark Arts (DA) and Kiji.
Full Aero damage is 14, half is 7, one-quarter is 3 and one-eighth is 1.
NIN 99/SCH 49 (Tarutaru; INT 107). Kiji has item level 113, katana skill +153. Base katana skill is 433 (417+16). I didn't have a negative control katana.
Code:
386 elemental skill; Kiji
Full: 27/30
1/2: 3/30
1/4: 0/30
1/8: 0/30
386 elemental skill; no katana
Full: 1/30
1/2: 1/30
1/4: 4/30
1/8: 24/30
149 elemental skill; Kiji
Full: 3/30
1/2: 0/30
1/4: 1/30
1/8: 26/30
149 elemental skill; no katana
Full: 2/30
1/2: 5/30
1/4: 3/30
1/8: 20/30
Raw data:
Code:
DA+Kiji Nothing DA+Kiji DA only
7 3 1 14
14 1 1 1
14 7 1 3
14 1 1 7
14 7 1 1
14 7 14 1
14 1 1 1
14 1 1 1
14 3 1 1
14 14 1 1
14 1 1 1
14 1 1 1
14 1 1 1
14 7 1 1
14 1 1 1
14 1 1 3
14 1 1 1
7 1 1 1
14 1 1 1
14 14 14 1
14 1 1 1
7 1 1 1
14 1 14 1
14 1 1 1
14 3 1 3
14 1 3 1
14 1 1 1
14 1 1 3
14 7 1 1
14 1 1 1
So "hit" rate is bad until Kiji is added on top of 386 elemental skill (from active Dark Arts) so this is consistent with the idea that additional magic accuracy comes only from the item level weapon and native weapon skill contributes nothing. (Note: Hit rate is bad with Kiji and capped katana skill with 149 elemental skill, suggesting native or base skill has nothing to do with magic accuracy. Ok, so I don't have a negative control with no katana skill whatsoever but I'm not getting on the test server to check that.)
This can explain previous observations. For example, Soothsayer Staff is ilvl 113 with 162 staff skill whereas Izhiikoh is ilvl 119 with 242 dagger skill. Whatever the magic accuracy difference is between the two, taking SE at its word it's not surprising to me that there were fewer resists with the dagger independent of differences in base/native combat skill between the two weapon types, as previously weapons with higher ilevel tended to have more macc than those with lower ilevel (Tamaxchi being one notable exception). (We need some evidence to determine that magic accuracy increases only from the item level weapon. Technically I haven't shown that affirmatively but if I were to get on the test server and zero out katana skill, I'm confident I would get mostly unresisted nukes with Kiji and Dark Arts. If I get around to it)