We have noticed that the Breeze icons used by the kcm modules in system settings are not the same size. For example the Color and Fonts icons use small circular icons. Look at the general appearance of the icons in system settings in KDE4, Mate, Cinnamon, GNOME, OSX and even Windows.

When a user enters the system settings area for administration, one would expect the icons appear symmetrically the same. For example. openSUSE's Yast has always used icons that were symmetrically the same. Whether in GNOME, KDE, Mate or Cinnamon they have a finished professional look to them.

Perhaps you have some new ideas for an upcoming version of Plasma 5.5 or higher to fix the icons used by the KCM modules.

Icons in System Settings are exactly the same size. By default System Settings uses 32 px icons and this can be changed by the user. The ones in Breeze currently are 32 px. You can open the files yourself and check.

Some are wider to keep the aspect ratio and with the absolute exception of the keyboard icon for Shortcuts they all have the same height.