This is something of a nitpick, but I'm having some trouble getting to grips with tikz-cd. I'm not sure of the TikZ terminology, but I think I'm trying to find a way to manipulate cell widths. Here's a minimal example to illustrate my problem:
\documentclass{minimal}
\usepackage{tikz, tikz-cd}
\begin{document}
\begin{tikzcd}
A \rar \dar & B \rar \dar & C \dar \\
D \rar & E \rar & F \oplus G
\end{tikzcd}
\end{document}

I'd like to make the arrow from B to C the same length as that from E to F+G. My first thought was that I should pad the box (cell?) containing C so it's the same width as the one containing F + G. I can sort of do it by replacing C with \quad C \quad, but surely there must be a better way! Does anyone know how to do this?


