Reduce aircraft low altitude status vs MANPADS

I believe the hovering/flight height for an aircraft to be considered "low altitude" should be reduced for the MANPAD.

For context - I had a match last night on liberation peak where a chopper was farming kills by hovering over the hill nearby capture point F. Our team was pushed back to F and E with our chopper spawn camped and no viable pilots to compete. 

Noticing the devastation I decided to swap to engineer and equip the Anti aircraft. Unfortunately my efforts were in vain because the target was considered low altitude despite being above and in clear view, and so the farming continued.

Nothing could be done even with weapons designed for this situation. Hillside in picture below. 

My understanding of a MANPAD was that they're designed to combat low-flying aircraft, helicopters, and UAVs. But in this situation nothing was working and I'm sitting there wondering .. what now?? It was definitely a useless feeling. 

May as well grab some popcorn and watch the carnage from a safe distance. Unless ofc you like being the fish in the barrel. 

Now I'm all happy for the missile to go off target if the pilot did evasive maneuvers such as LOS or low flying at speed, but at least allow me to get a lock to make them buzz off for a moment. 

I would rather it act as a deterrent instead of being just useless in this situation.