The "banzai" incoming spell cast status affects the casting unit's target instead of the spell cast target from the combat log. I suggest using the combat log event's cast target instead.

To clarify, this is common in arena when the opponents are using arena1/2/3 and focus macros.

Not possible. The point of using the enemy target to guess the spell destination, is that combat_log does not provide the target information for players in SPELL_CAST_START events (blizzard removed that information from combat log some years ago).

OK, I see what you mean. I tested this in-game and checked the combat log events to confirm what you've said. Thanks for the clarity.