(6) Where, owing to a special relationship between the payer and the beneficial owner or between both of them and some other person, the amount of the royalties paid exceeds, for whatever reason, the amount which would have been agreed upon by the payer and the beneficial owner in the absence of such relationship, the provisions of this Article shall apply only to the last-mentioned amount. In such case, the excess part of the payments shall remain taxable according to the laws of each Contracting State, due regard being had to the other provisions of this Convention.