3. Upon receipt of an application pursuant to paragraph 2, the national regulatory authority shall assess whether the roaming provider has established that it is unable to recover its costs in accordance with paragraph 1, with the effect that the sustainability of its domestic charging model would be undermined. The assessment of the sustainability of the domestic charging model shall be based on relevant objective factors specific to the roaming provider, including objective variations between roaming providers in the Member State concerned and the level of domestic prices and revenues. The national regulatory authority shall authorise the surcharge where the conditions laid down in paragraph 1 and in this paragraph are met.