Cannot change certain font's size after unicode-font-setup

[amosbird]

    (unicode-fonts-setup)
    (dolist (charset '(kana han cjk-misc bopomofo))
      (set-fontset-font (frame-parameter nil 'font) charset
                        (font-spec :family "WenQuanYi Zen Hei" :size 13)))

I'm trying to decrease the font size of certain charset. But the above elisp doesn't work.