Wireless Joint

You're looking for the hardware design guide, reference RF ports. Other than that a general idea of what it does during operation.
I'll be at my office pc in about two hours. I'll link and explain what I think when I get there.

The modem uses the main and div ports for all general LTE transmissions. It only uses the two mimo ports for mid and high band frequencies (MHB: 1452–2690 MHz), and only under load, AND only on towers that support 4x4 MIMO engagement. The Main and Div will support all frequencies (~600-6000 MHz)

Generally all 4x4 antennas use four identical elements placed in different rotated positions.