Now I understand what you mean. You don't need to set the Force talker alias to network setting.
Both callsigns need to have a registered and valid DMR ID. If the openSPOT4 receives a call from a C4FM transceiver, then it looks up the source callsign in the DMR ID database, and if the callsign-ID pair can be found in the database, then it will use that DMR ID as the source ID for the call.
Make sure the callsign set in the transceiver exactly match the registered callsign (don't use special characters, or whitespaces before or after the callsign).