Using Particle System Instance Parameters in C++

I am having difficulty correctly setting particle system instance parameters in C++. It seems that my actors are not getting set correctly.

I’m trying to convert the beam tutorial to C++. The only step that’s tripping me up is setting the “BeamSource” and “BeamTarget” instance parameters via code. Note: I can drag my particle system into a level and hook up the source/destination and it works as expected.

I’m calling this on my particle emitter:

for (UParticleSystemComponent* emitter : particles)
    emitter->SetActorParameter(TEXT("BeamSource"), previousSegment);
    emitter->SetActorParameter(TEXT("BeamTarget"), segment);

Where previousSegment and segment are the source and target AActor’s in my scene.

I can then set a breakpoint and look at emitter->InstanceParameters and confirm that the Actor field is no longer a NULL pointer. But if I then go into the particle settings and turn up my source distribution vector constant, I see my particle system change, despite its source method being Actor.