Sensitivity to cross section curves

GH, as previously mentioned, gave new cross section curves to Anna, and I have been examining the sensitivity to the "dipsy doodle" today.  Here is a plot of the three cross section curves I have tested:

The results are puzzling to me.  I expect the green curve to produce the most signal, the red an intermediate amount, and the blue the smallest.  This is not exactly what I am finding, oddly.  Here are the results for the ratio of Be9/Al:

And of course the control is the same for all three curves, which were all run at an input velocity of 2.9e7 cm/sec.  The signal curves alone look as follows:

The only thing I could think of was that although the cross section curves appear to be the same at low energies, in fact they are not.  This is born out, and explains the trends.  What we learn here is that the most important place to measure the cross sections with fidelity is at the lowest energies (which is not surprising given that this is where they will overlap with the doppler shifted 14 neutron spectrum).  Here's a plot to convince you:

This makes it clear that red should give less signal than blue, even though after 14.8, the cross section is larger.    Green wins because of the dispsy doodle.  Cross sections are apparently critical to this measurement.