I've seen that happen alot If I spawn too near the IP or come in at an angle too extreme for it to get stabilized for a good run.
It basically ran out of time to get within proper constraints for the drop before it reached the drop point. It is circling around to get lined up better for another run.
Just as a test, try increasing the initial leg before the drop wp further out and make sure there is sufficient distance between the drop WP and the actual target triangle. Like at least 10 nm I think.
Sorry, I was just being a goof.
Not sure of the answer to your question. You might see if something called Skynet could help. Its a script to simulate a networked coordinated IADS. Maybe that could be adapted to you needs. https://github.com/walder/Skynet-IADS
Though sounds like you have a simpler solution.