The arena setting is acutally called "ManuverKillRange". You will be awarded a maneuver (or proxy) kill if the following conditions are met:
1) The enemy was not damaged by another player who is still "in sortie".
2) You are within ManuverKillRange of them when they either: Bail, are killed, are captured, disconnect.
3) You are the closest enemy player to them.
Perk points are not awarded for proxy kills.
If you pinged them before they crashed, you are awarded perk points, and it's not considered a proxy kill.