Custom formula based on total sale

Hello,

I am creating a custom rate based on a formula.
My current formula is referral_rate*product_commission. “referral_rate” and “product_commission” are custom made variables created by the following rule:

function my_variables( $variables, $rate, $context ) {
$vat_rate = 0.055;
$product_total = $variables[’t’]*$vat_rate;
// FIXME: Find sale total
$sale_total = $product_total;
$variables[’vat_rate’] = $vat_rate;
$variables[’product_total’] = $product_total;
$variables[’product_commission’] = $variables[’t’]*0.21;
if($sale_total >= 3000){
$variables[’referral_rate’] = 0.25;
}else if($sale_total >= 5000){
$variables[’referral_rate’] = 0.3;
}else if($sale_total >=7000){
$variables[’referral_rate’] = 0.4;
}else if($sale_total >=10000){
$variables[’referral_rate’] = 0.5;
}else{
$variables[’referral_rate’] = 0.2;
}
return $variables;
}
add_filter( ‘affiliates_formula_computer_variables’, ‘my_variables’, 10, 3 );

$product_commission – commission available for the affiliate
$referral_rate – rate applied based on the sale total amount vat included

In order to calculate the referral_rate I need to check the sale total amount. However since the referral are processed by product sold, I am unable to do that.
There is any information under the variable $scope or any other place that I can check for this information.

Thanks in advance,
Vania.