Sounds like maybe its going too fast. This is what I found on it:
<max-detection-rng-nm type="int">28</max-detection-rng-nm>
<weight-launch-lbs>425</weight-launch-lbs>
<weight-warhead-lbs>87</weight-warhead-lbs>
<drag-area type="double">0.349</drag-area>
The thrust is classified, but its maximum speed should be mach 4 + the aircraft speed. So just increase the thrust until it reaches that speed around its maximum range.
Notice about maximum detection range, that 28 miles is under ideal conditions. Meaning the target is 28 miles out, but flying straight at you without big maneuvering. So maybe you should use around 20 miles for testing when it reaches mach 4 + aircraft speed.
And make sure its thrust duration is long enough to reach that. I am guessing 100-120 seconds, but you will have to experiment with that.