Gnuplot：垂直未对准钥匙盒和钥匙标签

我有以下gnuplot脚本：

#!/usr/bin/gnuplot

set terminal pdfcairo font "Latin-Modern-Roman-Bold,25" size 5,3
set output "tmp.pdf"

set tmargin 2.0
set bmargin 1.2

set offset -0.3,-0.3,0,0

set ylabel "X-Axis" offset 2,0

set xtics out nomirror offset 0,0.65 #rotate out nomirror

set yrange [0:1]
set ytics .2,.2,3 nomirror

# Select histogram data
set style data histogram
set style fill solid 1 border lt -1

set key reverse at 6.5,1.22 horizontal width 0.5 sample 2

set style line 3 lt -1 lc rgb 'yellow';
set style line 2 lt -1 lc rgb 'red';
set style line 4 lt -1 lc rgb '#008080';
set style line 5 lt -1 lc rgb 'orange';

set style histogram gap 1

plot 'tmp.tsv' using 2:xtic(1) title "AA    " ls 2, \
     'tmp.tsv' using 3:xtic(1) title "BB    " ls 3, \
     'tmp.tsv' using 4:xtic(1) title "CC    " ls 4, \
     'tmp.tsv' using 5:xtic(1) title "DD    " ls 5, \
     'tmp.tsv' using 6:xtic(1) title "EE    " ls 6, \
     'tmp.tsv' using 7:xtic(1) title "FF    " ls 7

此代码生成以下输出：

为什么关键标签（即AA、BB、CC等）略低于各自的方框