i cannot see why either.
It works with two items at quantity 3 and 3 on my test.
Maybe one of the other calculations is causing a conflict? Try disableing all of the other rules in the shipping charges and taxes sections so that only this one rule is enables.
also, how is the $_SESSION['ttown6get1'] getting set?
<?php echo("session: ".$_SESSION['ttown6get1']); ?>
to the cart page to see what it's value is.