You are not using the functionality as designed, you are trying to force it to what you think you need. I recommend taking a step back and explain what the problem is you are trying to solve (XY Problem).
Do your methods contain the Attribute Set required? That is what will drive the PO Suggestions to purchase the correct attribute set. You need to forget everything you think you have learned about AUOM as you are not using it the way Epicor designed it.
If we start from scratch and I understand what you are trying to do, I believe we can get to the solution.