Our store uses USPS. We would like to charge different handling cost for some products depending on the destination country. I have the logic to identify the products. To check for the destination country I would like to use the following logic
if ($order->delivery['country']['id'] == '223' || $this->usps_countries == 'US') {

I need to know where the handling charge is calculated inside the USPS module so that I can change it? I am using version 1.3.9f