Adding some edits...

.plotstyle/final.mplstyle

@@ -33,7 +33,7 @@ xtick.minor.width:   0.4     # minor tick width in points
 xtick.major.pad:     3.5     # distance to major tick label in points
 xtick.minor.pad:     3.5     # distance to the minor tick label in points
 xtick.color:         black   # color of the ticks
-xtick.labelsize:     small  # font size of the tick labels
+#xtick.labelsize:     small  # font size of the tick labels
 xtick.direction:     in     # direction: {in, out, inout}
 xtick.minor.visible: True   # visibility of minor ticks on x-axis
 xtick.major.top:     True    # draw x axis top major ticks
@@ -54,7 +54,7 @@ ytick.minor.width:   0.4     # minor tick width in points
 ytick.major.pad:     3.5     # distance to major tick label in points
 ytick.minor.pad:     3.5     # distance to the minor tick label in points
 ytick.color:         black   # color of the ticks
-ytick.labelsize:     small  # font size of the tick labels
+#ytick.labelsize:     small  # font size of the tick labels
 ytick.direction:     in     # direction: {in, out, inout}
 ytick.minor.visible: True   # visibility of minor ticks on y-axis
 ytick.major.left:    True    # draw y axis left major ticks
@@ -81,7 +81,7 @@ legend.shadow:        False    # if True, give background a shadow effect
 legend.numpoints:     1        # the number of marker points in the legend line
 legend.scatterpoints: 1        # number of scatter points
 legend.markerscale:   1.0      # the relative size of legend markers vs. original
-#legend.fontsize:      small
+#legend.fontsize:      None
 legend.labelcolor:    None
 legend.title_fontsize: None    # None sets to the same as the default axes.
 

defs/Helper.py

@@ -22,14 +22,14 @@ import matplotlib.pyplot as plt
 ### ----------------------------------------------------------------------------------------------------------------------------------- ###
 ### Helper.py
 
-def quick_plot_setup(fontsize = 6):
+def quick_plot_setup(fontsize = 8):
 
     plt.style.use(r'C:\Users\tschan_d\Documents\code\.plotstyle\quick.mplstyle')
     matplotlib.rcParams.update({'font.size': fontsize})
 
     return ".pdf"
 
-def final_plot_setup(fontsize = 12):
+def final_plot_setup(fontsize = 8):
 
     matplotlib.use('pgf')
     plt.style.use(r'C:\Users\tschan_d\Documents\code\.plotstyle\final.mplstyle')
@@ -42,7 +42,7 @@ def final_plot_setup(fontsize = 12):
                                 'xtick.labelsize':  fontsize,
                                 'ytick.labelsize':  fontsize,
                                 'pgf.texsystem':    r'lualatex',
-                                'pgf.preamble':     #r'\usepackage[fontsize = ' + str(fontsize) + r']{fontsize}' + 
+                                'pgf.preamble':     r'\usepackage[fontsize = ' + str(fontsize) + r']{fontsize}' + 
                                                     r'\usepackage{unicode-math}' + 
                                                     r'\usepackage{accents}' + 
                                                     r'\usepackage{fontspec}' + 
@@ -53,9 +53,11 @@ def final_plot_setup(fontsize = 12):
                                                     r'\usepackage{siunitx}' + 
                                                     r'\usepackage{mhchem}' + 
                                                     r'\newcommand{\der}[1]{\ensuremath{\textnormal{d}\,{#1}}}' + 
-                                                    r'\renewcommand{\normalsize}{\fontsize{6.000000}{6.00000}\selectfont}'})
+                                                    r'\DeclareSIUnit\ppb{ppb}' + 
+                                                    r'\DeclareSIUnit\ppm{ppm}'})
 
-    return ".pgf"
+    # Exporting via the pgf backend produces some font issues, therefore outputting via pdf is most consistent...
+    return ".pdf"
 
 class DATFile():