Looking at the front of a BlueROV2 Heavy with the Tracker 650 mounted on the bow facing forward. Note the arrow pointing to the starboard side of the ROV; if the the arrow was pointed up the cable would project below the bottom of the ROV, and if the arrow was pointed down the cable would interfere with the electronics enclosure. Since this is not the default orientation you will need to send a command (only once since it will be stored in non-volatile memory) with parameters (90, 0, 90).
Iso view of the mounting in the previous figure: the front of a BlueROV2 Heavy with the Tracker 650 facing forward. Note the arrow pointing to the starboard side of the ROV. The battery tube can be shifted aft to provide clearance and improve balance.