The setup we had for whole HiMo corn was a Herc unloader with a Boot in the middle to throttle the flow.  We always left the short (not mini) arm on and would not move it till the end.   
Our current setup uses the Goliath forage unloaders with the forage chains (minus some diggers).    The arm needs to advance to reduce the chance of large air pockets.   If the rolled/ground grain has a large difference in moisture, the arm moving becomes very important.   We learned that one.  
We put a few wrinkles  in one of our silos when we filled a new year's wet corn on top of the previous year's dryer corn.   The dryer corn flowed ok without the arm moving (corn was coming out,, no problems,, right??)  and it created some air pockets.  Now it is just as simple to make sure the arms moves, no matter what is going on.  We have 3 20x70's that we use for grain.

Bill