Alternate Sales Amount & Commissions on Billings?

Looking for some help as we seemed to have hit a bit of a standstill in our exploration of commissions schedules and alternate sales amounts.

We have been trying to work on using the built-in fields for commissions purposes, and moving off of calculating permissions on average cost, rather on item defined costs.

We set item-defined costs, added the Estimated GP and other fields to the sales order, set the preference to calculate through the sales order (under Setup), etc. We then had to script the ASA to be equal to the Est GP, because the system won't use that field, so we wrote a script to trigger afterSubmit to perform a search on the transaction with the Est GP in the results and then setting the Alternate Sales Amount equal to that (which was not so straightforward, being that the field is not exposed in SuiteScript). In any event, we have that