Vendor commission wrong

The only commission we charge our vendors is the Stripe fees, which is 1.4% + 20p per transaction.

So I put through a test transaction, with 2 items total and 3.99 postage, a total of £15.98. So the fees in stripe were £0.42.
However in wcfm its showing as £0.61.

I have added the following lines to my functions.php file but it still seems to be off by a bit.

add_filter( 'wcfmmp_order_item_quantity', function( $quantity, $product_id, $variation_id, $item_price, $vendor_id, $order_id ) {
	return 1;
}, 50, 6 );
add_filter( 'wcfmmp_is_allow_commission_on_tax', '__return_true' );
add_filter( 'wcfmmp_is_allow_commission_on_shipping', '__return_true' );

Any idea what im doing wrong?