gnuplot: bar charts visualization

My gnuplot script plot a bar graph for 2D data either in monochrome or color format:

set term pngcairo size 800,600
set termoption noenhanced
set tics font "Helvetica,10"

#set xtics noenhanced
set ylabel "Fraction, %"
set xlabel "H-bond donor/aceptor, residue"
set yrange [0:1]
set ytics 0.1
set grid y
set key off
set boxwidth 0.9
set style fill solid 0.5

# TWO OPTIONS FOR BAR VISUALISATIONS!! NB: ADD HERE TRIGGER FROM COLOR_DATA TRIGGER
# 1 - use it with non-colored bars"
#plot "\$data" using 0:2:xtic(1) with boxes, "" using 0:2:2 with labels offset 0,1
# 2 - or use it with colored bars:
plot \$data using 0:2:3:xtic(1) with boxes lc rgb var, \
        '' using 0:2:2 with labels offset 0,1

The problem when I have just one bar, one the graph it occupiers all the graph on X:

Would it be possible to set some minimum dimension for the bars to make the dimensions of a single bar similar for a situations with two bars, for instance:

Solution

My understanding is the following: if you have only one box:

maybe gnuplot tries to autoscale and the automatic boxwidth is small relative to the autorange (hence just a thin line).
if you set a certain boxwidth, autoscale with scale to the given boxwidth (hence the graph filled with the box).
you could set a fixed xrange, but then you are loosing the benefits of autoscale. Instead you can use set offets (check help offsets).
if you have more than 1 box autoscale will work.

Script:

### boxwidth with boxes style
reset session

$Data1 <<EOD
 1   Abc
EOD

$Data2 <<EOD
 1 Abc
 2 Xyz
EOD

set style fill solid 0.3
set key out
set rmargin screen 0.7
set yrange[0:]
set ytics 0.5

set multiplot layout 4,1

    plot $Data1 u 0:1:xtic(2) w boxes ti "No special settings"

    set boxwidth 0.9
    plot $Data1 u 0:1:xtic(2) w boxes ti "set boxwidth"

    set offsets 1,1,0,0
    plot $Data1 u 0:1:xtic(2) w boxes ti "set offsets"

    set offsets 0,0,0,0
    plot $Data2 u 0:1:xtic(2) w boxes ti "more than 1 box"

unset multiplot
### end of script

Result: