Discount of subtotal exluding tax

Hi

I have been attempting to work out how to use your plugin to display the discount based on the subtotal minus tax rather than including it.

I had hoped that this might do the trick:

protected function calculate_discount( $value, $subtotal_ex_tax ) {
		if ( strstr( $value, '%' ) ) {
			$value = ( $subtotal_ex_tax / 100 ) * str_replace( '%', '', $value );
		}

		return $value;
	}

Basically replacing $subtotal with $subtotal_ex_tax but it doesn’t seem to make any difference.

Any suggestions welcomed!

https://www.ads-software.com/plugins/woocommerce-payment-discounts/