Does anybody perhaps have further information on the actual physical attack formula? From my basic testing using the very early team against the Mist Shade, magic attacks are completely consistent according to the formula listed on the site. Physical attacks, however, were all over the place. This also goes for Unite attacks. You can also notice variation on enemy attacks. Thus I think the actual physical attack formula is something like:
DAMAGE = (((Offense_ATK * FURY_MOD) + RAND(3:8)) - Defense_PROT ) * ATTACK_MOD
Consider the Mist Shade case. His listed PROT is 10, meaning any incoming attacks should have a flat reduction of 10. A level 2 Riou will have either 16 or 17 STR and a WPN bonus of 5, giving his total ATK of about 21. By most logic, he should do 11 damage against the Shade.
However, out of 7-8 attempts for this, Riou managed to deal damage in the range of 14 to 17 damage pretty consistently. One case is that the Mist Shade's listed PROT is slightly off, but the variation range still implies that some randomness affects the final damage. I think I remember seeing something like this when I was debugging some other battle formulas, but I didn't pay much heed to it. This is also backed up by similar tests with Bolgan; with an ATK of 32, Bolgan would do between 26 and 30 damage.
Unite attacks also get an odd treatment in this regard. I had one case where the Circus Attack Unite did 132 damage against the Mist Shade. On a different use, it did 164. A swing of 32 damage is pretty huge; normal calculations say the attack should do 152 damage with all the characters' strengths taken into account. For this to happen, the random extra damage would need to cover a range of at least 6 and apply to each character individually before the 2x multiplier is applied. This makes the damage fairly unpredictable.
It should be noted that this doesn't happen at the high end. For example, using Kindness Rune glitch to get 999 ATK causes that character to always hit for the same amount of damage, at least from what I've seen. The damage exactly matches what it should be according to the given formula too. So this means that the 999 cap is applied after any additional random damage is added to the attack. This is also true for specialty rune attacks, like Shin's Spider Slay.