I would leave well alone, personally I would have authorised the refund of $7 straight away if I had no proof of posting to Paypal's standard, it is very unusual for Paypal to fight a chargeback unless you insist and the cost of that insistance is $15. They will usually either refund from your account or from their own pocket if you have seller protection. Are you sure they did actually fight and win the chargeback dispute or are they just giving you a discretionary rerfund?