After much experimentation. I found the NTC solution for Emolie and 5761, and that can be translated to a Li-ion build too.
First the NTCs,
SL12 1R010, have a a 20% tolerance. That is huge.
Second the NTCs are very reactive and sensitive to temperature and slight changes in internal resistance and slight changes in circuit Amps.
The NTC will become more resitant when the Amps or temperature drop or other things decrease circuit resistance, like adding resistors or other NTCs in parallel.
Adding more than two in parallel or series you likely will defeat the purpose and they will not work.
Therefore I found that I had to test the lights used fully assembled. I mount NTCs in the tail cap with an inline fuse. Using two pieces of copper wire I wrap the bulb pins and stick them into the socket and from these extensions hook up a meter. Since I put charging jacks into the lights I could hook up to the socket and measure Vbattery quite easily.
I found that the slight differences from an assembled light and testing the circuit on just jumpers would cause significant differences in the NTC behaviour. In the light they acted more like the theoretical equations, outside they always were too high in resitance.
At 5 amps I was getting 0.06 resistance or close to it and that is spec.
With the emolie I found my current 5761 were flashing at just about 7.09 volts. Ouch, look at the pile at 5-6 dollars each.
I used many different Ametherm NTCs too.
Using a resistor in series was necessary to bring the emolie voltage down to Vbulb at 7.0 when the NTC reached steady state. 0.09 ohms and the NTC would flash and read 7.4 Vbulb. Vbattery was 7.6 volts. I needed to drop 0.4 volts more and add .08 ohms resistance. That figured to a 2 watt .18 (calls for a .17) total resistance in series with the NTC.
Put that in and it worked. The out put depends on the Vbattery but the drop is about .6 volts when fully charged.
It is by the eye brighter than the A123 driven 5761s and at the level of the D Lion driven 5761.
I do not use a NTC with that one but have a Batteyspace PCB on the pack after stripping the OEM PCBs. The PCB somehow behaves just enough as a soft start that I have no flash problems with that build.
So my suggestion is to suck it up and build you light. Start with the 12SL1R010 and a .10 resistor in series if you are using the 7.2 volts on Li ions or .18 ohms if on the 7.4 emolie and then take some readings off the bulb. Resistors are cheaper than bulbs, you can fine tune in this way. You may loose one or two bulbs but I have given you the starting point.
In all cases since I use the tail cap for the NTC, there is no spring resistance in these mods.
Good luck.