Can't make/receive Wifi calls on cellular ipad that has no cellular plan

I have a cellular IPad Air 2 running iOS 13.4. Unlike a NON-cellular iPad, this cellular iPad doesn't seem to be able to make/receive WiFi calls on its own. I tried removing the SIM card, but, still, the ONLY way this iPad can make/receive phone calls is when my iPhone is on.

I have another non-cellular IPad Air 2 and that non-cellular iPad can make/receive wifi calls just fine without the iPhone needing to be turned on.

What I would like to accomplish is have this cellular iPad Air 2 behave the same as the non-cellular iPad Air 2. (after all, I have no cellular plan for this cellular iPad and removed the SIM card)

I did enable WiFi calling by pressing Upgrade to WiFi calling in Facetime settings, but this still required the "calls from iphone" setting to be enabled first, and anytime "Calls from iphone" is enabled it always tries to call from the iPhone which only works if the iPhone is on. It is never able to utilize WiFi calling without the iPhone being turned on. If "Calls From iPhone" is off, then the call button is disabled in Contacts. (presumably because the SIM was removed, and this iPad is behaving like there is no such thing as actual self-contained WiFi calling)

How do I accomplish WiFi calling on the cellular iPad air 2 WITHOUT the iPHone being turned on? Keep in mind that a non-cellular iPad Air 2 is able to make/receive WiFi calls even when the iPhone is off. Thanks.