In a WHMCS template how can you determine if the logged-in user is a User on the account, and not the primary account holder?

[Bodes]

In a WHMCS 8.11 Smarty template, these variables return information about the Primary Account Holder, even if its a sub-user account that's logged in:

{$clientsdetails.firstname} 
{$clientsdetails.lastname}

How can you determine if it's actually a sub-user logged in, and then retrieve the firstname, lastname, and email of the sub-user, not the primary account holder, as seems to be returned with the above variables?