Forex Spot & Foward

We can make Spot transaction in sap like below.

For example, we created spot transaction like a "Buy HKD and Sell USD" . (Local currency is JPY )

After settle and run TBB1 and TPM18 , we can see 4 document ;Sell,Buy, Forex loss & gain.

But the amount of Forex loss & gain is too much.

We can not understand the reason.

Could you explain the reason?

And please let me know the reason and how we can fix this.

Thank you in advance.