I don't now, but I will have shortly. I am going to be airlayering a large cork oak in about 4 weeks. Because I have never airlayered a cork oak before, I hesitate to comment until I know what I did worked. I will take extensive photos and post results.
Oaks are notoriously difficult to layer. I've heard of it done but many more cases where it failed. Some that had success recommended leaving a "lifeline" bit of bark intact rather than encircling the entire branch as is normally done.
I once airlayered an English Oak. I did it in May, and removed the layered portion early September. It was the most perfect layer that I've ever seen, with a perfect nebari all-around. It was 15 years ago, and I still have the tree. This year I planted it back into the open ground, for a couple of more years, in order to thicken the surface roots.
Here are two photos of the Cork oak that I have. I think that I have two possible choices for design here with #1 being a upright design using the straight part of the trunk and #2 using the curve and removing it at the point where it tapers off.
The base of the tree is 5.5 inches and the trunk just above that is close to 3 inches.