Event definitions do not work on projectiles

I am trying to create a custom projectile, I want the entity that hit the projectile to have the tag "hit" added, but when I tried to do it and put "affect_target": true, "affect_projectile": false, "affect_shooter": false. the event was still executed to the entity and not to the one that hit.

"on_hit": {
    "impact_damage":

{         "damage": 4,         "knockback": true     }

,
    "remove_on_hit": {},
    "definition_event": {
        "affect_target": true,
        "affect_projectile": false,
        "affect_shooter": false,
        "event_trigger":

{             "event": "spell",             "target": "self"         }

    }
}