Jimmy. wrote:RC is 9 hole, ~250mm long
I think that's your issue. Mine is 85 mm long with 5 x 3/4" internals. It needs copper scrubbers (mesh) inside the internals but it works beautifully with a gate valve. Change to a needle valve and it should give you the control you need.
Or cut your RC in half. :?
RCs only need a trickle going through them when collecting product but usually full flow is required for full reflux. Mine didn't hold full reflux with 2000 W without the copper mesh.