There is often this "confusion" with Bridges.
2 3CX Systems when bridged integrate so nicely and seamlessly that a lot o people start thinking that they should behave as if they were 1 PBX.
This is not true.
2 Bridged 3CX systems are 2 separate systems, they just integrate very nicely. That is why they have 2 different License Keys, FQDNs, Management Consoles, etc.
Calls from a Bridged PBX ARE external.
Have you considered keeping just the 1 PBX and users from the 2 locations connect to the same PBX? You would probably have to increase the hardware specs and License Key of this 1 server, but that would possibly solve your problem.
For IP Phones, at the location where the 1 PBX is, you could put an SBC to make things easier.
Even more, you could move this 1 PBX to the Cloud and then both locations would connect to it to the cloud,so a possible internet outage at the "main" location would not affect both.
I know this is not what you asked about, but it's a possible idea that could solve your problem at the same time.