It actually encourages the behavior.
The bulk of the behavior you are describing is not encouraged by proxies, it is encouraged by players wanting to survive. The vast majority of people are NOT doing this as a primary means of getting kills. They are not going to suddenly start deciding to stick around and fight it out just because their ack won't give them a proxy kill.
If they don’t then at least they aren’t rewarded for the behavior.
Have you considered that
the proxy announcement may not be designed as a reward but as a deterrent? If you have for this reason decided not to follow people into ack, as you claim, then
perhaps it is working as intended.
If removing it will encourage more people to fly into enemy ack, then perhaps that is why it remains.There are ways to force a situation where someone doesn't have the time or the inclination to run to their ack. If you are having trouble engaging people with a Pony before they can get to ack, it may be something you want to explore. That is something you CAN control, whereas other player's behavior you cannot.