Line type U and Back order

Hi

I am using JDE 9.1

I am using line type - U and want SO to cnacle the line when stock become zero. But I do not want SO to go on hold or cancle when line is stock - i do not want Back order to be create at all. I keeped allowed Back order flag at item master and customer master as it is requirment.

Now, when i create the SO, I want U line type item to cancle the line and S line to not go on Back order id stock is zero. I am using PO in commintment option is set as 2 .