Adding Single UFH with own valve

Hi, I wondered if anyone has had experience with adding a separate BDR91relay for controlling a zone valve for under floor heating?

I’m fitting and plumbing a new system, the configuration I have on evohome is a new valve zone for the UFH but it’s also triggering the heat demand on the rad valve. Any idea if i can rework it to only trigger the UFH relay when setting the temp for the UFH zone?

Thanks
Mark