tw_ee_sage_pay_form_filter.php

<?php //Please do not include the opening PHP tag if you already have one.

add_filter('FHEE__EE_Form_Section_Proper___construct__options_array', 'tw_ee_sage_pay_form_filter', 10, 2);
function tw_ee_sage_pay_form_filter( $options_array, $form ) {
    if( $form instanceof EE_Billing_Attendee_Info_Form 
        && $form->payment_method() instanceof EE_Payment_Method  
        && $form->payment_method()->type() === 'Sage_Pay_Server' 
        && !empty( $options_array['subsections'] )
    ) {
        $options_array['subsections'] = array(
            'country' => $options_array['subsections']['country'],
            'state' => $options_array['subsections']['state']
        ) + $options_array['subsections'];
    } 
    return $options_array;
}