Series 4 (unlike Series 3 and older) and iPhone X both support Bluetooth 5, which has a much longer range.General BlueTooth range is usually about 30 feet or so (but obstructions like walls can reduce that).
The AW will connect also via known Wifi (ones your iPhone has already connected to) to extend that range.
As long as the watch is connected to wifi, it doesn't need to be in range of the phone.Undecided about GPS+LTE or GPS. How close does the iPhone need to be to the watch to provide coverage for making and receiving calls? Thanks.
I had a similar issue with slow connection speed. In my case I had to add my 802.11n (2.4GHz) wifi network name to my wireless networks on the phone. The watch won't connect to 802.11ac (5GHz) networks. I assumed it was connected because the wifi icon in control center on the watch was blue, but it wasn't actually connected - just "on".FWIW, I've had a heck of a time getting Audible books to transfer to my S4 from my iPhone X. It's only worked for me when they're basically next to one another, and charging. Neither is technically a requirement but that's what I had to do. Granted, these are very large files, so perhaps the connection is more sensitive than it would be for other types of transfers/connections.