I just tried that. Left my phone at home, drove to my parents and checked their iPhone if they can locate me on my watch.
Turns out they can see my iPhone left at home, but I didn't share my watch location with them.
So I opened the "Find People" app on my watch, taped on "Me", then on the name of the family member -> share location and selected the name from the contact list.
After that my Apple Watch was visible in the "Find My" app on their iPhone under "Devices -> "Ingo's Devices"
This worked on their Wi-Fi network and without the Wi-Fi enabled on my watch, connected to LTE
Since this happened to you on your brand new 11 and Ultra 3 Series, this might also be related to the software on these watches, if you have no restrictions set up.