Hello,
What do you mean by a subset of antenna ports?
If you are referring to using a few of the mobile antennas, it is advised to use all of the ports connected to an antenna, as that is how the modem module is designed to operate and using 3 of 4 or even 2 of the 4 ports might result in an unsatisfactory or even unpredictable performance in terms of mobile connectivity.
If by a subset you mean using all of the mobile antennas and neither of the WiFi ones, that should cause no problems at all, no port terminations are necessary.
Best regards,