For optional prayers that are prayed in units of 2 rak’ahs in the 3rd/5th/etc rak’ah, should the opening supplication be made between the takbeer and recitation of Surah Al-Fatihah?

If the Salaah of 3 rak’ahs   is made in a continuous form without a break or salaam after two rak’ahs, then there is no need to recite the opening supplication in the third rak’ah because the Salaat is continuous. However, if there is a salaam after two rak’ahs  and the person gets up to pray the remaining rak’ah as a single unit like in the case of Witr, then he or she can make the opening supplication.