How to *set* INCOMING IP address [BGP]?

Hello, as you may know, I've had a case about setting up outgoing IP address to use BGP router ID, the response was here and here. So I disabled the NAT on this interface, and for now, it shows correctly outgoing address from the network like A.B.C.190 but every incoming traffic that I see is exactly A.B.C.190, not the real IP address like 1.2.3.4, 8.8.8.8, 11.15.13.12, 62.12.233.15 etc... so it is very hard to monitor this. Of course on Fortigate I can see the Source and Destination, but when the traffic goes to LAN it always is A.B.C.190 from the Internet.

Thanks in advance for replies.