It's probably hard to measure the temperatures accurately. In pizza ovens we talk about three different modes of heat. Conduction (through contact with the stones), Convection (through the hot air) and Radiation (through the heat radiating from the fire and all surfaces).
Enzo Coccia explained in a video I saw that a pizza is baked through all the above modes of heat, the bottom mostly through conduction, the cornicione mostly through radiation and the toppings mostly through convection.
Trying to point an IR gun at a metal surface is likely to give an inaccurate reading as it reflects a lot of heat and the IR gun isn't really made for measuring that, it will be most accurate when used on the stone. Some IR guns allows to change something called the emissivity factor, which allows it to be more accurate when measuring certain materials.
The mouth of the oven is very large compared to it's size, so I think it's very likely that you lose a lot of heat just from hot air exiting and cooler air being pulled into it.
If a steel gives you the result you want, then that seems to be the best solution, and 3 minutes makes for a very tasty pizza, they don't all have to be Neapolitan!
I like the browning on the bottom of your pizza, though the cornicione looks a bit anemic. Maybe some more flames would balance the heat out better.
