As the saying goes, “I am glad you asked that question.” The short answer is “Yes,” there is a designated minimum air space in the code.
Many years ago when I was still in school, I had to fight for good grades like everyone else. The problem in my math classes was not just getting the answers correct, but providing the necessary proof for the answers. The teachers did not seem to appreciate my knowledge (or maybe it was my explanation) that if I gave them my proof, I would have to shoot them. I could see their displeasure by the drop in my grade. They finally wore down my resistance, and I decided to see reality and provide the proof with my answers.
To find the entire answer, we go to Chapter 12 of TMS 402-13. The actual name is Building Code Requirements for Masonry Structures, but you will find I use “TMS 402-13” or the “Code” because it is shorter.