As I was assembling the circuit, I didn’t have the 5.1k resistor specified for R4 in series with the RV1 trim pot, so I went to revisit our calculations to see if a more common 4.7k would do, and I noticed that we might have forgotten to figure in the approx. 1mA flowing through R4 and RV1 in our computations.
So we might not have that “1mA to spare” after all.
I would recommend going with 220 ohms for R26
It gives us (11.5-10.667)/220 = 3.8mA which is 1mA for the TL431, 1.3mA for the circuit, about 1mA for R4&RV1, and 0.5mA to spare.
I’ll be using 220 ohms for R26 and 4.7k for R4