I'm doing shipping by weight using the USPS module but the shipping charges for USPS to mexico seem really high, $19 when calculated by the module but going to the post office its like $10. The normal inside the US calculates almost double so for $1.51 in shipping it calculates it as $2.50 thats not a big deal because that kinda covers packaging costs but is that the same problem its doubling it to mexico?