Whether the pillar 3a contribution should be allocated exclusively to Swiss taxable income or proportionally between Swiss and French earned income.
Pillar 3a contributions are general deductions with a sufficient link to earned income, but in international allocation they must be deducted proportionally according to the Swiss and foreign earned income; they are not allocated exclusively to Swiss income.
Because the contribution is not calculated as a percentage of income but is a voluntary, capped payment, and international deduction allocation should avoid over- or double deductions. The FZA social-security coordination does not change the tax allocation rule.