How to clamp a PolylineArrow to ground when stored in primitves collection


I am trying to clamp a polyline arrow to the ground when adding to a polyline collection stored in the viewer’s primitives collection.

simple reproduction of problem. Please ignore the visual distortion / glitchiness. Apparently it’s a known issue with polylineArrows, but I don’t see that on my application, so it’s not an issue for me: Cesium Sandcastle

If I cannot use the clampToGround property to acheive this, can someone please tell me a way I can “flatten” my positions to make them have an altitude of 0?

Thank you in advance for any help you can offer!