GMX Energy with multiple error blocks

GROMACS version: 2020.2 cpu
GROMACS modification: No

My understanding is that when I run gmx energy without -nbmin or -nbmax options, the error is calculated for a moving block average of 5. When I run over a range of options (e.g. -nbmin 5 -nbmax 50), still only a single error is reported so I was unsure what this value corresponded to. Naively, I expected the error value to increase, corresponding to the plot in figure 4.4 of a statistics resource (4.8 Statistics), however the error has decreased in all of the ranges I’ve run. Thanks in advance for your help.