The basis of assessment for the withholding tax provided for in 1° of 2 of article 204 A on the income mentioned in article 204 B is made up of the net amount taxable for income tax on the sums paid and the benefits granted, before application of article 80 sexies, the second sentence of the first paragraph of 1° of Article 81, 3° of the article 83 and the second and last paragraphs of a of 5 of the article 158.