Comparison: If you pull an enemy to first position (e.g. Harpy Eagle) when the 1st position is empty, the other enemies remain in their positions, BUT if the 1st position is occupied then ALL other enemies are shuffled down 1 slot even if they don’t need to. E.g. if the formation was [A _ C D] and you pull D to first, the result is [D A _ C] not [D A C _].
In this case, if the enemy formation is (say) [A _ C D] and A shuffles from Terror, the result is [C _ A D] not [_ A C D] ? I could see an argument both ways here. On one hand, this guarantees that when Terror procs this will always result in a shuffle (increasing its utility similar to normal shuffles), but on the other, it suggests that the last surviving Troop of a team may flee regardless of their position in the lineup when the official announcement suggests that this should not be the case:
The term “Position” has traditionally only been used in the context of “pull/push an enemy to first/last position” and always refers to slot #1 or #4 regardless of whether it contains a Troop or not. It is not the same as “first/last enemy” (which ignores empty slots).