Phone calls don't notify on Vivoactive 5 in Vibrate mode

If I set my phone to vibrate only, all other smart notifications seem to come through on my watch, but phone calls don't unless I have audible ringing enabled.

This is not what I was expecting to happen, is this a bug or expected behaviour, or (hopefully) is there a way round it?

Phone: Samsung A25, Android 14

Vivoactive 5 version 9.27