Yes, generally port forwarding is only from the external address to internal addresses. I'm guessing a commercial-grade router could be programmed to do what you want, but not any home router I've ever seen.
You should be able to use the router's external address from inside the network though (i.e., send packets from 192.168.1.300 to 42.1.98.9:10443 and it should redirect to 192.168.1.200:10443).