In the production module the costing sheet creates a pre calculation based on the costing sheet including overhead based on surcharges. The production posting also creates indirect postings. This is independent of the active cost principle chosen for the items. (e.g. FIFO or Std cost) On purchase orders this principle only works for standard cost based items. I suggest to introduce costing sheet with overheads also on purchase orders for other cost principles. At least this could be parameter in the inventory model for the items.