Okay here is my vortex / pie pan experiment.
The initial setup. Note that I do not place each individual briquette. I've used the snake method a few times without having to do that. But I think it's important to use Kingsford briquettes and that they are all touching in at least two places. There are fresh Kingsford briquettes from an almost-new bag. See the tumbleweeds. This set up will give me two burn paths on either side of the center.
Pizza pan diameter of 19.25 inches placed on top with the lip up.
Then the grate. This is the cheapest Weber grate I have out of five.
Let's add some wood chunks. I'll put a mesquite chunk by the start of the fire followed by plum wood.
It's gettin' late. Let's start the fire.
So far so good. Now the wing sections and my long stem dial thermometer
Now we'll close it up and wait. Bottom vents wide open. Top vents wide open. I expect to have to close down the bottom vent some when it begins to approach 225. Ambient temp is 53 F.
I also added a little dial thermometer over the top air vent, a Thermoworks Smoke air probe dangling down from the top vent to the grate, and another through the probe port into the biggest wing section.
So how did it turn out?
IT WAS A DISASTER.
Probably the worst cook attempt I've ever tried going back forty years!
Here's a recap of all the things that went wrong.
1) It took WAY TOO LONG to get to temp. After an hour, it was only at 154 F with all vents open. After two hours, it was at about 215 F.
2) The wing sections did NOT cook correctly. When checked with my Thermopen One, after two hours, it showed a temp at the top of about 155, but as I pushed it in deeper and deeper, the temp kept dropping until it hit 120 F and came out the bottom of the wing! In other words, it was not cooking all around, it was cooking from the top down. Why? Obviously because there is not enough air between the grate and the pan. And of course, there was not enough hot air circulating around the cook area.
3) When I gave up and removed the grate and pan, only one of the two burn paths were lit correctly. The left one that was lit was fine, burning coals and following along the path. The other one on the right was barely smoldering. It seems the two burns competed with each other for oxygen, and after one became dominant, it starved the other one.
How to fix this?
1) Forget about the tumbleweed start up. It works fine for cooking low and slow in a SnS or with a pile of charcoal on one side and the food on another (classic indirect). But this system here, tumbleweeds are way too slow. Use a chimney or a torch to light the charcoals.
2) The burn paths need to be set up differently. I've used two and even four burn paths successfully in the past (no pie pan) but I think aligning the start path with the three vents would work much better. In other words, set up three burn paths aligned with the three bottom vents and make them thicker. OR just do one giant burn path as briefly illustrated in the Weber vid.
3) The burn paths need to be placed closer to the bowl which would provide even, smooth air flow from the bottom vent, through the lit charcoal, and around the outside edge of the pan.
4) There needs to be more space between the disk and the grate. Mine only had about a half inch. The grate was actually sitting on the pizza pan lip. Also, as it turns out, my medium sized Vortex is just under five inches high which puts the top of it right at the grate. In other words, the medium Vortex which is designed for the 22" Weber sits too high for this application. Lifting the cook grate somehow would be helpful.
5) The Weber product is only 18.25 inches vs my 19.25 inch pizza pan. It's possible that's part of the problem.
6) I believe the sharp angle of the Vortex may cause some disruption of smooth air flow. Note that the Weber cone is much closer to vertical. Charcoal needs to be placed closer to the bowl and not up against the vortex.
7) If you have a fan/blower to blow air into the bottom vents or through a bottom smoke hole, it would likely solve a lot of these problems.
8) Or just get the Weber product.
Good luck