Hi there
When you do a physical settlement the price in the trade is taken as a fix price. To adjust the FX rate from the trade versus the book value you have to run TPM18. The price is always coming from OB08. Please check the currency pairs.
When you execute a cash settlement the rate is given by the business partner you traded with. This is only used if the currencies are "NDF = non deliverable forward". The settlement then takes place in a currency where payments can be done. If you trade USD/INR the settlement is done in USD.
Kind regards
Juerg Heiz