OOOH...
Experiment time.
Engineers like to simplify the problem (works great with spherical cows in a vacuum?). In more solid cases like this, experiment is better.
Make 2 6"x6" square of each design. Place a hot piece of metal (around 130 F) with a thermocouple in between the two and throw it in your freezer. Time the temp drop to 80F. Whichever is slower is the better insulator.
Here's a dual channel thermocouple that can measure both (assuming that you use identical metal pieces) at the same time.
A simple fix would be to trade these switches out for manual "infinite" switches. A quick search turned up this page: http://www.theceramicshop.com/store/category/39/207/Switches-Relays/
Alternatively, if you only wish to bisque in this kiln, turning on each element one at a time will ramp the temperature. I would start with each element turned on one hour apart and go from there. Thermocouple monitors are inexpensive on Amazon as well. I own this monitor: https://www.amazon.com/Signstek-Channel-Digital-Thermometer-Thermocouple/dp/B00FFYEPVQ/ref=sr_1_2?ie=UTF8&qid=1476032393&sr=8-2&keywords=thermocouple+reader and while the thermocouples that come with it are useless in a kiln, a couple of type K eight gauge thermocouples are very cheap and easy to install, this will read them accurately.
Another option would be to use the guts of this kiln and install solid state relays, controlled by anything from a raspberry pi to a PID controller. This isn't as difficult or expensive as you might think, though you have to be into DIY stuff and willing to learn a few things.
DAMN THEY ARE PROUD OF THAT !!!
I paid $30 GBP for the Dohicky from Russ, and $18 USD for the meter on Amazon, https://www.amazon.com/gp/product/B00FFYEPVQ/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
For your testing, you are not looking for a reading, you are looking at the change in readings between start and finish.
Have at least a gallon bucket of water and leave it at room temperature over night. Next morning do your readings with his test pattern in 5% increments all the way to 100%, best three of five. The few tests you do over your working current aren't going to hurt anything. When you find your power and or mA working range, then do that 10% in 1% increments to get it exact.
For me, my 80W tube should max out at 24mA. Testing with the Dohicky let me know that I hit my 80W almost dead center between 23mA and 24mA. So my max current is now 23.5mA. I hit that mark at 63% power on my RDC 6445G. I hit it at 64% power on my old Top Wisdom controller.
That test will also tell you what your actual power curve is, and EVERY tube is different. Even knowing that all tubes have a curve and are not linear in any way, I was disappointed to find my power curve was more like a quarter circle. Luckily I do very little engraving, but knowing my actual power curve told me just how difficult it might be if I really wanted to do it.
There are guys with 100W tubes with a flatter power curve that can do better engraving than I can with my 80W. It's pot luck stabbing in the dark if you don't know your power curve.
Drop Russ a comment on his YouTube video with your email address. He'll remove your address and contact you directly to get a Dohicky coming your way. He's in the UK, and it still only took two weeks for it to get here in the mail.
If you can afford it (say $70) - don't get a Thermapen, get a K Type thermocouple brain and a food-grade submersible probe.
The brains are universal and cheap (and read up to two probes independently)
The probe looks like this:
Apart from these two pieces, you need a 9V battery. Some 3M foam tape is also good if your dad does Sous Vide. These thermocouples allow for constant probe readings the way you'd use an old fashioned roasting probe, except you can use this under water, in oil, in a smoker, on a grill, in a fridge, or in a pan. For things that overcook quickly or are blind cooked, this is the best thermal tool you can get right now.
Do you need that many channels? I would go with something simple this if you don't need to centralize a bunch of inputs.
If you don't need USB (logging/monitoring) you could use something like this instead.