Place an empty either a HEMTT or Zamak, either variant and name t1.
Place a group of 16 units, name the group test.
Preview and run
terminate h;
h = [] spawn {
{
player sidechat format ["pos = %1",_foreachindex];
_x assignAsCargoIndex [t1, _foreachindex];
_x moveInCargo [t1, _foreachindex];
sleep 1;
}forEach units test;
};
From the debug console, notice the empty cargo index's as explained above.
For the Zamak's try
player assignAsCargoIndex [t1, 6]; player moveInCargo [t1, 6];
and notice you will be placed inside the cab at the same position as cargo index 0.