The optimum voltage is around 1 volt. This is where the three series, blue, pink, and red, are closest to each other on the plateau.
These are the values for the graph above. Three seperate test were made using mulitple counters. Counters one, two, and four were used in the first two tests and counters one, two, and five were used in the third test to plateau counter one. Included are the counts per minute for the coincidence for each run.
Counters two and four were set to a voltage of 1.106 volts and kept constant. Their coincidence was measured three times, when counter one was at 0.749, 1.351, and 1.660 volts. The counts per minute were 552, 567, and 565, respectivly. The average was 561 counts per minute.
Counters one and two were set to a voltage of 1.110 volts and kept constant. Their coincidence was measured three times, when counter one was at 0.944, 1.241, and 1.543 volts. The counts per minute were 559, 574, and 567 respectivly. The average is 567 counts per minute.
Counters one and two were set to a voltage of 1.103 volts and kept constant. Their coincidence was measured three times, when counter one was at 0.741, 1.050, and 1.337 volts. The counts per minute were 703, 718, and 693, respectivly. The average was 705 countst per minute.
With not too many short pulses, giving the desired Gaussian distribution it looks like this is the optimum voltage. This study was run at 0.996 volts.
Note: This is the same study as shown for counter one in the single counter plateauing.