SO entry preferencing

Hello

I am trying to setup soft commit and would like when entering a SO for the branch plant to auto populate and go through my preference hierarchy. I would like to have it go look at available qty in my hierarchy and then if qty still left and not filled, SO back order it to a certain plant. I have tried several different setups but cannot get it just right. See below one of the setups

in this setup, I have 1000# avail at UTH and 500# avail at UJO, Order is for 2000#. I would like when entering the SO in P4210 it grabs the 1000# from UTH and creates a shipment number, then split the line and go find the 500# at UJO and create a shipment number, then backorder the remaining 500# at UTH. Right now in this scenario it will create line 1 from UJO (not sure why when UTH is first in hierarchy), then line 1.001 at UTH then backorder at Corp-US which is not even in the pref