There is no unit cost show in Stock Ledger report if keyin Stock Return (-ve QTY) in Sales Invoice Screen
Sales invoice screen does not cater for Stock Return, user got to keyin in Sales CN for stock Return.
Another solution is, keyin the stock return in Cash Sales as it cater for Stock Return Design (Except for Serial no. return)
select the debtor, tick 'Post to debtor Account'
This is because Cash Sales allow to keyin Walk in customer (save transaction without select the debtor) thus this screen design can be insert the -ve qty and the cost will be updated.