I think I'm seeing what the problem may be with the "thump" when we raise the actuator on the ZX-1. Although the anti-tilt height adjustment is between 1 and 2 inches of the backrest rigidizer bar (as documented), it is hitting the Tishaft Back release bar. I can even see where the anti-tilt wheels have rubbed off the paint. I think we will need to adjust the height about .5-1".
I remember when ordering the ZRA I wished we could have given a backrest rigidizer bar placement height so we could make sure it was a bit higher. I think we will have only a small margin for this adjustment. It may be something worth considering for others ordering a new chair for use with the ZX-1.
I made a video with Rob in the chair and also without him in the chair in case anyone is interested. It shows the ZX-1 Power Add-on Anti-Tilt mechanism hitting the back release bar on a TiLite ZRA.