The letter listed examples of drone use, including in the case of a 5-year-old child held hostage in an underground bunker in Alabama earlier this year.
But Paul said last week the new information was not enough to answer his questions.
Paul first issued a letter about drone surveillance last month asking Mueller about the FBI's policies. When he received no response, he sent a second letter on July 9, saying he would object to the consideration of Comey as Mueller's successor until he received "adequate answers" to his questions.
The FBI sent two responses this month, one classified and one unclassified.
In the unclassified version, the FBI went on the record about the 10 cases of drone surveillance. The FBI also maintained that it would acquire a warrant before using a drone when the suspected individual has a reasonable expectation of privacy.
Paul sent a new letter on Thursday, asking for more clarification on the FBI's understanding of a "reasonable expectation of privacy."
"I am concerned that an overbroad interpretation of this protection would enable more substantial information collection on an individual in a circumstance they might not have believed was subject to surveillance," the letter stated.
He also pressed for copies of educational and training material the FBI uses on such matters.