Tikz: Arrow description closer to arrow

Question

I want $Q(g)$ closer to the diagonal arrow in this tikz-picture. How can I manage that?

Thanks.

\begin{tikzpicture}[description/.style={fill=white,inner sep=2pt},baseline={([yshift=1.5em]current bounding box.south)}]
              \matrix (m) [matrix of math nodes, row sep=2em,
              column sep=3em, text height=1.5ex, text depth=0.25ex]
              {
                        Q(I^\pr) & Q(\quot{B}{B^\pr}) \\
                        Q(I) & Q(B)\\
              };
                    \path[->,font=\scriptsize]
                    (m-1-1) edge node[auto] {$Q(f)$} (m-1-2)
                    (m-1-1) edge node[auto,swap] {$Q(\iota^{I'}_{I})$} (m-2-1)
                    (m-1-2) edge node[auto] {$Q(g)$} (m-2-1)
                    (m-2-1) edge node[auto,swap] {$\bar{f}$} (m-2-2)
                    (m-2-2) edge node[auto,swap] {$Q(p^{B}_{B/B'})$} (m-1-2)
                    ;
  \end{tikzpicture}