Well I can't explain that one and throws my theory out as well. $40 is better than $20 though so I suspect neither of us is complaining!
This hello fresh offer has been perfect timing as last week received a "We miss you 50% Discount" if I reactivated which worked out to be $69 for a family 4 meal box, then got the Amex $20 rebate on top. This weeks order will be over $100 so will see what rebate is this time.