669.5. If a testamentary trust receives, in a taxation year, an amount under an income-averaging annuity contract respecting income from artistic activities, that amount is deemed, for the purposes of paragraphs c and d.1 of section 312 and section 1129.68, to be an amount received at a particular time by a particular beneficiary under the trust, and not to have been received by the trust, to the extent that the amount may reasonably be considered, having regard to the circumstances and the terms and conditions of the trust arrangement, to be paid or payable at the particular time to the particular beneficiary.