the size is defined in sources/rb-source.h
#define RB_SOURCE_ICON_SIZE GTK_ICON_SIZE_LARGE_TOOLBAR
but only a few elements are really depending on this size. And some elements don't have the proper icon to use at 16ps. It is just a big mess. I thing this bug would go as "don't fix".
the size is defined in sources/rb-source.h SIZE_LARGE_ TOOLBAR
#define RB_SOURCE_ICON_SIZE GTK_ICON_
but only a few elements are really depending on this size. And some elements don't have the proper icon to use at 16ps. It is just a big mess. I thing this bug would go as "don't fix".