Can't find any manual about changing width of taglist element size. Taglist element is wider than icons I had set. It looks really awful =(
Screenshot: http://s12.postimg.org/fkva7xywd/Screenshot_16_02_2014_16_04_07.png
Taglist element consist of icon, text and gap between them. This gap defined in awful.widget.common.list_update function in line
m = wibox.layout.margin(tb, 4, 4)
Despite you have no text, double gap is still here. To solve this problem you can copy list_update function to your rc file, fix it and send as fifth(!) argument in awful.widget.taglist.