Critical Ring's "Instant Death"

Another strange thing is I cant seem to get the instant kill effect to activate on my Aran while attacking more than 1 mob. Ive only seen it activate when attacking one enemy with my aran, with the exception of the combo skills (smasher, peril ...) While I have seen the instant kill effect on Battleship Torp. On another note I am paying attention to what # hit is the instant kill and it seems to always be the 1st hit in a set of multiple attacks (1st hit of Cannon's 4 hits) If the ring only calculates instant kills per attack, then it wouldn't be the most hit based attacks that would be getting instant kills often such as TT with its 6 stars would only count as 1 attack (roughly 90 attacks per minute), where SoA (Hurricane) or Rapid Fire at 500 attacks per minute should. Just a theory for now: but this may be difficult to test without a substantial amount of statistical data # of instant kills per attacks vs # of instant kills per hits.