Change the default behavior of \\ inside cases environment?

Question

Based on the answer by egreg in The curly brace is too big, I would like to modify the cases environment

After some experimentation, I found out the following option that I like the most:

\documentclass[10pt]{article}
\usepackage{amsmath}
\usepackage{lmodern}
\usepackage{setspace}
\onehalfspacing
\usepackage{etoolbox}
\begin{document}
\makeatletter
\patchcmd{\env@cases}{1.2}{0.9}{}{}
\makeatother
\begin{equation}
P^(A) = \begin{cases} 
1 & \quad \omega_0 \in A, \[.6ex]
0 & \quad \omega_0 \notin A.
\end{cases}
\end{equation*}
\end{document}

My question is: how can I make \\[.6ex] the default behavior inside cases environment?

Answer 1

I guess you want something else than 0.9.

\documentclass[10pt]{article}
\usepackage{amsmath}
\usepackage{lmodern}
\usepackage{setspace}
\onehalfspacing
\usepackage{etoolbox}
\begin{document}
\subsection{No patch, no optional argument}
\begin{equation}
P^(A) = \begin{cases} 
1 & \quad \omega_0 \in A, \
0 & \quad \omega_0 \notin A.
\end{cases}
\end{equation}
\subsection{Patch, no optional argument}
\makeatletter
\patchcmd{\env@cases}{1.2}{0.9}{}{}
\makeatother
\begin{equation}
P^(A) = \begin{cases} 
1 & \quad \omega_0 \in A, \
0 & \quad \omega_0 \notin A.
\end{cases}
\end{equation}
\subsection{Patch, optional argument}
\begin{equation}
P^(A) = \begin{cases} 
1 & \quad \omega_0 \in A, \[.6ex]
0 & \quad \omega_0 \notin A.
\end{cases}
\end{equation}
\subsection{Different patch, no optional argument}
\makeatletter
\patchcmd{\env@cases}{0.9}{1.1}{}{}
\makeatother
\begin{equation}
P^(A) = \begin{cases} 
1 & \quad \omega_0 \in A, \
0 & \quad \omega_0 \notin A.
\end{cases}
\end{equation}
\end{document}

So you probably want, before \begin{document},

\makeatletter
\patchcmd{\env@cases}{1.2}{1.1]{}{}
\makeatother