Following the approach suggested in post #30, I've derived the range equation as r = rb sqrt(Ev2) / ( sqrt(Ev1) - sqrt(Ev2)) where r is the range from light source to nearest LDR, rb is the baseline (addition range to 2nd LDR), Ev1 is the illuminance at the first LDR and Ev2 at the 2nd LDR. Assuming I've done this correctly, it confirms my sense that the intensity of the light source isn't a factor (in an ideal sense anyway, it will matter given the finite sensitivity of the sensor).
Ev at a sensor goes as 10^(m log10 (VoR1 / Vin - Vo)) +b) where m and b are parameters of the LDR, Vo is the output of the voltage divider, R1 is the fixed resistor in the voltage divider, and Vin is the voltage across the voltage divider. See https://www.allaboutcircuits.com/projects/design-a-luxmeter-using-a-light-dependent-resistor/ for basis.
I also played a bit with an LDR and a single lamp in a darkened room and the resistance vs range appears to be a smooth function of range and seemed relatively insensitive to aiming when pointed generally in the direction of the light. There was a small but noticeable AC component on the ADC measurement when looking at the compact fluorescent bulb light source. Hopefully that isn't significant if the two LDRs are measured in rapid succession. I'll have to scrounge a bit to find reasonably matched LDRs or face a daunting calibration process to proceed further.