Generally, for a kill to work, the kill must originate from the same or greater tier. So if a Tier 2 player tries to kill a Tier 1 player, the kill will fail. If a Tier 1 player tries to kill a Tier 1 player, the kill will process. This occurs before passives, so if power levels do not allow for a kill, passive abilities, with some exceptions, will not affect whether the kill succeeds or fails.