code:

        // Draw a beam from the emitter to us, using our particle system.
        // First, update the path they'll follow. Waypoints are in reverse order
        // (i.e. particles end at waypoint 0). Waypoint 0 ends at plane position
        var planePos = leash.plane.transform.position;
        leashPath.m_Waypoints[0].position = planePos;
        leashPath.m_Waypoints[2].position = leash.origin.transform.position + Vector3.up * 250;
        leashPath.m_Waypoints[1].position = (leashPath.m_Waypoints[1].position + leashPath.m_Waypoints[2].position) / 2;
        // HACK just trying to get CinemachineSmoothPath to behave
        leashPath.m_Waypoints[1].position = (leashPath.m_Waypoints[1].position + leashPath.m_Waypoints[2].position) / 2;
        leashPath.m_Waypoints[3].position = leash.origin.transform.position;
        leashPath.InvalidateDistanceCache(); // HACK: otherwise path gets really weird in the middle

        if (particles == null || particles.Length < leash.effect.main.maxParticles) {
            particles = new ParticleSystem.Particle[leash.effect.main.maxParticles];
        }

        int numParticles = leash.effect.GetParticles(particles);
        float maxAge = leash.effect.main.startLifetime.constant;
        for (int i = 0; i < numParticles; ++i) {
            float t = particles[i].remainingLifetime / maxAge;
            particles[i].position = leashPath.EvaluatePositionAtUnit(t, CinemachinePathBase.PositionUnits.Normalized);
            particles[i].velocity = leashPath.EvaluateTangentAtUnit(t, CinemachinePathBase.PositionUnits.Normalized).normalized * leashPath.PathLength / maxAge;
        }
        leash.effect.SetParticles(particles);