I'm with Dustin on this, at least from a purely best-insulation perspective.
Caveat: as others have pointed out, there is a substantial benefit to placing the CCF under the air pad -- you get an added layer of protection / insurance against your air pad going flat. That's certainly something to consider.
But to answer your question from purely a warmth perspective ... and phrasing it a bit more simplistically than Dustin ...
Consider the problem in the same way as you'd consider insulating your body with clothes, such as a puffy jacket, or in the same way as a sleeping bag surrounds your body. In the BPL community I think we're a little more familiar with the scientific perspective on that issue because of the detailed articles that have been published here over the years covering that topic.
The primary idea with insulating garments / sleeping bags is that you create a cavity of air around your body. The body pumps heat into that air mass, slowly raising the average temperature. Hopefully the layer of insulation that is directly outside that air mass is doing its job and preventing the air mass from losing that heat to the outside world -- that would be by preventing radiative, convective, conductive, and sometimes evaporative heat loss.
Most critically now, consider this: hopefully the air mass around your body is not so large that your body struggles to heat it up efficiently. This is why it's important that our sleeping bags are cut trim enough that there isn't a bunch of extra unused air space inside the bag with you -- that would make you COLD even if the bag was good otherwise. The same is true for puffy jackets -- even if the seal is good at the cuffs and the hem, if your jacket is sized way too large for you, you'll feel noticeably colder inside, because the internal air mass that you're heating up is larger than it otherwise would be.
Make sense so far?
Now then ... consider an air pad. For the sake of demonstration we'll consider a purely air-filled pad such as a Big Agnes Air Core or that kind of thing. Basically this is a large, shaped, plastic ziploc bag full of air. It has almost no insulative value, because the air inside the pad is free to move around, rather than being kept still. If we were to consider an analog to an air pad in the clothing world, it would be something like a pool floaty -- a plastic inflatable jacket-like thing, filled with nothing but air.
Conversely, consider a CCF pad. Very different! A CCF pad also has tiny air pockets in it, but since those pockets are CLOSED (CCF) the air is held very still, and the insulative value-per-thickness is much higher than with an air pad. To what can we compare a CCF pad if we want to find an analog in the clothing world? My best guess would be like a thin neoprene wetsuit.
Finally ... let's consider that if we had an all-inflatable jacket, made of the pool toy kind of material, and we also had an all-neoprene jacket, made of wetsuit material ... how would we want to layer these? For the sake of experimentation, let's assume that (somehow) the fit for these two garments is the same ... regardless of how we layer them, they will fit properly.
So do you put the neoprene on the inside or the outside?
For anyone that's ever put on a wetsuit before, the answer is pretty easy. Putting closed cell foam next to your skin makes you VERY WARM, very quickly. That's because the air mass trapped next to your skin is minimal, so it takes almost no time for your body to raise the temperature of that air mass.
By contrast, if you were to put the pool toy jacket on the bottom, next to your skin ... your body would be heating up 1" or 2" of surrounding freely-moving air space, quite a bit more than what was trapped by the wetsuit. It would take much longer to feel warm in that getup, because it would be so much less efficient for your body to heat that larger air mass.
Whew ... this post grew long quickly. Anyway, I think I've gotten the idea across. Having CCF next to your skin should feel noticeably warmer, and faster.