After entering value of PrePosting in Purchase Requisition line (for a non-inventory part) and Purchase Order Line which is generated from purchase order, only M91 transaction does not have a value entered in Pre-Posting. But M92 is having this option. 

When we check the basic data setup it shows as follows:

However customer is having following business requitement. 

Customer  implementing a project in the company whereby the enterprise site 1 is being split operationally.
Work tasks and purchase orders are still raised under enterprise site 2, but at a pre postings level customer will have different values to represent the two separate entities within.
Subsequently on the pre postings the code part b (site) value will contain site 1 or site 2 values which are copied across from the work task to the purchase order lines.
M92 is correctly pulling the pre posting site value from the PO receipts; however there is a disconnect with M91 since this is not using the same value and instead is using the enterprise site value.
The impact is that Finance cannot reconcile based on these differences.

Please consider on implementing the “pre posting “ option to M1 posting control also.