Thanks Yuniar I slogged through it myself and got it working. For others ..this appends the email addy from the current form (id=2) to the redirect url which is another form(id=1).
post-functions.php
$process_result['form_redirect'] = $form_redirect . '&email=' . $table_data['element_2'];
where element_2 is the email field in the current form.
You then need to edit your view-functions.php file to accept the added parameter and populate the desired field again in my case the email addy.
On line 1682 you will find this code:
$element[$j]->default_value = htmlspecialchars($row['element_default_value']);
Right below that line, add this code:
if($form_id == 1 && $row['element_id'] == 2){
$element[$j]->default_value = $_GET['email'];
}
Again you need to edit the form_id and element_id numbers to match your "receiving" or redirected form.