just my 2 cents cuz we were discussing this spell in another thread.
I would definitely have to disagree that the ranged attack for harrying fire which is a physical action would be any different than the physical action of casting the TkP spell. You cast the spell as a standard action which includes making a ranged attack roll to hit with said projectile, the projectile being the weapon, the roll is a mental part of the casting of the spell it does not count as a separate action. I don't see how that would be any different if you are using it as a covering fire action rather than an attack action.