How to split ASCP/MRP demand between 2 suppliers?

Hi, I am having trouble solving the issue of split sourcing through ASCP.

My desired outsome is to split all supply requirements for an item between 2 suppliers in every planning run, not a split equal to our sourcing rule over the planning horizon.  Example: if the planning requirements are for 10 widgets, ASCP would suggest 2 purchase requisitions, 5 for Supplier A and 5 for Supplier B.

Here are the steps I have taken:
1) setup the item as purchaseable, etc and assign to appropriate inventory organizations
2) created a sourcing rule with both suppliers listed with rank 1 and Allocation 50%
3) created an Assignment set tying together the item and Item-Instance and Sourcing Rule