TL; DR: Use an old iPhone to create an extended BT hub for homekit accessories.

I've seen some people complain about this, such as the smart lock on the Bluetooth front door for the homekit, because of the distance to the homepod, which was very far from the front door.

The solution is simple and I just discovered it with a Vocolink BT contact sensor. It is my first BT homekit device.

The device must not be within the BT range of the HomeHub, but must be within the BT range of SOME iDevices that are connected to your homekit hub.

So if you have an old iphone SE (first generation) or even a 5s (it might even work on an iphone 5 on iOS 10, I don't know, I only had one SE and 5s to test) lying down, log in to an iCloud account, give that iCloud account access to your homekit, turn it on Wi-Fi and turn on Bluetooth, then set it closer to your BT homekit device that get a flash connection. Then plug it in and forget about it.

Does this work for other Bluetooth things, such as Hue bulbs? I doubt it. I assume this only works with ACTUAL BT homekit devices.

But if you want to make it work a really long distance, take the old SE, put in a SIM card, and you may need to connect it directly to the iCloud account that Homekit is enabled on, I'm not sure. But it could probably be a thousand miles away from your home hub and still register as part of it. Too bad it doesn't work with wifi.

But having an old iPhone lying around acting as a BT extender node and potentially a Siri node makes things work better.