بسم الله الرحمن الرحيم
A person who pays his Sadaqat al-Fitr as per the price of wheat his Fitrah shall be paid without any aversion. However, if someone is rich enough and pays it as per raisin and dates instead of wheat or pays one sa’ instead of half then it is better as it shall be more benefitting for the poor and the payee shall get more reward. If you have paid your Fitrah as per the cost of wheat then also your sadaqah was paid without any doubt, you need not worry. (From: Abu Dawud, vol. 1, p. 229, Bazl vol. 6, p. 454, pub. Beirut)
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.