How do I tell Siri which device to use?

So, I'm working in my office on the iMac. I have my iPad on the desk using it as a screen for my CCTV outsider as I'm expecting a delivery. I have my iPhone in the desk in case I get a phone call and the HomePod is in the corner.

When I say "Siri play ... such and such music" it's hit and miss as to which one responds. Is there a way to make one device dominant?