Voltage drop across ballest resistor

RustyRatRod said

I always thought a resistor had a set voltage drop regardless of voltage in. I guess that's not right.

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The first main thing that is set is the wire construction. Each material and size/gauge is cataloged at a per inch ohms resistance at 68 degrees. Additional graph charts provide resistance at other temperatures. These resources provided for any engineer building any resistor.
This ballast resistor has a specific total length of a specific wire to provide a total end to end resistance at 68 degrees. Knowing the material temperature changes and resistance changes, thus more or less energy is converted into heat, the engineer had to determine what length of what wire would produce a desired variance and hold the variance within acceptable limits without manipulating the environment with heat sinks, fans, whatever. In this example, like many others, a simple ceramic encasement was a preplanned factor and it works. We'll never know how many different sizes/shapes of ceramic encasements, wires, assembly placements, etc.., were tested.
All we have is what the ohms test should show and their explanation of its need/function.