Please be aware that swaps for CORN are stated in terms of percentages as shown under swap type under specifications on your MT5 platform.
Example:
This means that the swap rate will be 21.31% of the live price on a pro rata basis for a buy trade and -27.28% for a sell trade.
Therefore, the calculation for swap fees based on your buy trade would be:
Current Price * (contract size * longORshort rate / 100 / 360
689.73 * (2 * 21.31 / 100 / 360) = 0.805 USD = 0.70 GBP
We hope this clarifies your concerns over swap fees for CORN.