# Increase space between groups with package nomencl & etoolbox

I am writing a document and I need to have a table of notations. I wanted to reduce its size while keeping a good space between the different groups. I understood that:

1. I can use \setlength{\nomitemsep}{-0.1\parsep} to reduce the space between lines
2. I can use \renewcommand{\nompreamble}{\small} to reduce the font size

But I fail to keep a decent space between the groups titles and the previous lines. For example here the space between "Group B" and "Line number 3".

How can I increase this space while keeping the space between each line small?

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\usepackage{nomencl}
\makenomenclature
\renewcommand{\nomname}{List of Symbols}
\renewcommand{\nompreamble}{\small}
\setlength{\nomitemsep}{-0.1\parsep}

\usepackage{etoolbox}
\renewcommand\nomgroup[1]{%
\item[\bfseries
\ifstrequal{#1}{A}{Group A}{%
\ifstrequal{#1}{B}{Group B}{{}}}%
]}

\begin{document}
\mbox{}
\nomenclature[A,1]{a1}{Line number 1}
\nomenclature[A,2]{a2}{Line number 2}
\nomenclature[A,3]{a3}{Line number 3}

\nomenclature[B,1]{b1}{Line number 1}
\nomenclature[B,2]{b2}{Line number 2}
\nomenclature[B,3]{b3}{Line number 3}

\printnomenclature
\end{document}