Weaponless Dmg Formula?

Stereo's data, cleaned up:

lv. 17, 78 str 22 dex +0 atk = 9-56
lv. 17, 78 str 22 dex +8 atk = 12-76
lv. 17, 79 str 22 dex +8 atk = 12-77
lv. 17, 80 str 22 dex +8 atk = 13-78
lv. 17, 81 str 22 dex +8 atk = 13-79
lv. 17, 82 str 22 dex +8 atk = 13-80
lv. 17, 83 str 22 dex +8 atk = 13-81
lv. 17, 83 str 22 dex +0 atk = 9-59

At least that's how I'm interpreting it as.