Hi Tim

My step downs work in both fabrication and Revit although I found it to be very frustrating to get them to work

I think you need to setup how the connector is drawn in fabrication

Attached is screenshots of my setup and how it looks when drawn

Also I don't use liner thickness setting but rather have a fixed step down size which may not be useful for you

That's about as much help as I can offer you im afraid as I don't know Revit very well but hope this helps