How to add new rate once GRN posted.

Question

ABC-Raw Material Case
Po raised for 110 kg with Rate is rs. 2/- per kgs.
Eg- Purchase Order created 110 kg,so PO value is 110 kg X 2rupee = 220 rupee.
At gate entry  is Net weight is 100kg,
      2 rupees each kg .So 100 kg X 2 rupee = 200 rupee
      Moisture is 42 % .
                                    GR quantity    = 100 – 42 = 58kg.
Now  we got goods receipt  quantity is made for 58 kg. Inventory will hit for 58 kg  but not on 2rupees,its recalculated on new value .
Now to match vendor invoice value need to recalculate asNew rate =  Net weight(at Gate entry) X Rate/GR quantity.200 / 58 = 3.448275862 and New rate is 3.448275862.
58kg X 3.448275862 = 200 rupees. So now inventory will hit on new value.
At the time of invoicing the difference amount between vendor invoice and our invoice receipt is 20 rupee will be increased and that amount debited in raw material variance expense and credited to vendor a/c.
But Problem is vendor is  not sending invoice at the time of material supplement .And because of this material is issuing to Production and stock reducing.So now my question how to hit Difference amount that is 3.448275862 - 2 = 1.448275862 rupee   at the time of Goods receipt in SAP.
Kindly suggest your valuable points.

Answer 1

OSS note 399906 - Valuation with deviating purchase order price unit explains the valuation logic.
And as always with moving average price, the value of the stock gets adjusted if the invoice value is different. The already done goods issues cannot be re-valuated, hence you get bigger deviations of the price fo your material and  the remaining quantity can get far apart from the PO price. 
But there is not much to do except you urge your vendor to send the invoice timely, e.g. by EDI.
Or you block the stock until the invoice is received, which is not good practice. Or you change your valuation logic to standard price and post all differences to a difference account