Strange alignment behavior of two numbered equations on the same line

Question

Considering my previous question at this link One or more equations (two-by-two on different rows) with an enumerate to the left and the another on the right, I have a strange alignment behavior of two numbered equations on the same line. In other words there is an overhang between the (0.0-3) and (0.0-4) equations.

How can the problem be corrected?

Here there is the MWE and the relative output:

\documentclass{book}
\usepackage[top=2.5cm,bottom=2.2cm,
            left=3.2cm,right=1.5cm,headsep=10pt,
            a4paper]{geometry}  
\usepackage{mathtools,amssymb}
\usepackage[svgnames, dvipsnames, table, x11names]{xcolor}
\usepackage{pifont}
\usepackage{tabularx} 
\definecolor{ocre}{RGB}{243,102,25} 
\usepackage{lipsum} %%%%%%%%%%% <--------- added 

%----------------------------------------------------------------------------------
%   Change number equations with sections
%----------------------------------------------------------------------------------
\usepackage{chngcntr}
\counterwithin{equation}{section}

\renewcommand{\theequation}{\thesection-\arabic{equation}}
\newcommand{\eqnnumsymbol}{\textcolor{ocre}{\reflectbox{\ding{228}}}}

\makeatletter
\newtagform{bbrackets}% <name>
  [\textbf]% Internal style
  {(}% Left bracket
  {\ifnum\pdfstrcmp{\@currenvir}{equation}=0
     \eqnnumsymbol%
   \else
     \ifnum\pdfstrcmp{\@currenvir}{align}=0
       \eqnnumsymbol%
     \fi
   \fi
   )}% Right bracket
\makeatother
\usetagform{bbrackets}

\begin{document}
\lipsum[5][2-3]

\begin{tabularx}{\textwidth}{@{}XXX@{}}
\begin{equation}
f(x + y) = f(x) + f(y),
\label{eqn:1}
\end{equation} &
\begin{equation}
f(ax) = af(x),\,
x,y\in V, a\in\mathbb{C}
\label{eqn:2}
\end{equation}
\end{tabularx}

\lipsum[6][8-9]

\begin{tabularx}{\textwidth}{@{}XXX@{}}
\begin{equation}
\overline{E}= -\overline \nabla \varphi-\frac{\partial \overline{A}}{\partial t}
\label{eqn:3}
\end{equation} &
\begin{equation}
\overline{B}=\overline \nabla \times\overline{A}
\label{eqn:4}
\end{equation}
\end{tabularx}
\end{document}

---

Output:

Answer 1

I wouldn't really expect these to be aligned as they have different sizes, however you can get a bit closer if you use m rather than p columns. I use tabular here as tabularx isn't really helping as you know in advance given XX that there will be two equal columns, so you may as well specify that directly.

\documentclass{book}
\usepackage[top=2.5cm,bottom=2.2cm,
            left=3.2cm,right=1.5cm,headsep=10pt,
            a4paper]{geometry}  
\usepackage{mathtools,amssymb}
\usepackage[svgnames, dvipsnames, table, x11names]{xcolor}
\usepackage{pifont}
\usepackage{tabularx} 
\definecolor{ocre}{RGB}{243,102,25} 
\usepackage{lipsum} %%%%%%%%%%% <--------- added 

%----------------------------------------------------------------------------------
%   Change number equations with sections
%----------------------------------------------------------------------------------
\usepackage{chngcntr}
\counterwithin{equation}{section}

\renewcommand{\theequation}{\thesection-\arabic{equation}}
\newcommand{\eqnnumsymbol}{\textcolor{ocre}{\reflectbox{\ding{228}}}}

\makeatletter
\newtagform{bbrackets}% <name>
  [\textbf]% Internal style
  {(}% Left bracket
  {\ifnum\pdfstrcmp{\@currenvir}{equation}=0
     \eqnnumsymbol%
   \else
     \ifnum\pdfstrcmp{\@currenvir}{align}=0
       \eqnnumsymbol%
     \fi
   \fi
   )}% Right bracket
\makeatother
\usetagform{bbrackets}

\begin{document}
\lipsum[5][2-3]

\noindent
\begin{tabular}{@{}*{2}{m{.5\textwidth}@{}}}
\begin{equation}
f(x + y) = f(x) + f(y),
\label{eqn:1}
\end{equation} &
\begin{equation}
f(ax) = af(x),\,
x,y\in V, a\in\mathbb{C}
\label{eqn:2}
\end{equation}
\end{tabular}

\lipsum[6][8-9]

\noindent
\begin{tabular}{@{}*{2}{m{.5\textwidth}@{}}}
\begin{equation}
\overline{E}= -\overline \nabla \varphi-\frac{\partial \overline{A}}{\partial t}
\label{eqn:3}
\end{equation} &
\begin{equation}
\overline{B}=\overline \nabla \times\overline{A}
\label{eqn:4}
\end{equation}
\end{tabular}
\end{document}

Answer 2

Thank you very much to @David Carlisle and @Marijn that with your comments I have had another possibility:

\documentclass{book}
\usepackage[top=2.5cm,bottom=2.2cm,
            left=3.2cm,right=1.5cm,headsep=10pt,
            a4paper]{geometry}  
\usepackage{mathtools,amssymb}
\usepackage[svgnames, dvipsnames, table, x11names]{xcolor}
\usepackage{pifont}
\usepackage{tabularx} 
\definecolor{ocre}{RGB}{243,102,25} 
\usepackage{lipsum} %%%%%%%%%%% <--------- added 

%----------------------------------------------------------------------------------
%   Change number equations with sections
%----------------------------------------------------------------------------------
\usepackage{chngcntr}
\counterwithin{equation}{section}

\renewcommand{\theequation}{\thesection-\arabic{equation}}
\newcommand{\eqnnumsymbol}{\textcolor{ocre}{\reflectbox{\ding{228}}}}

\makeatletter
\newtagform{bbrackets}% <name>
  [\textbf]% Internal style
  {(}% Left bracket
  {\ifnum\pdfstrcmp{\@currenvir}{equation}=0
     \eqnnumsymbol%
   \else
     \ifnum\pdfstrcmp{\@currenvir}{align}=0
       \eqnnumsymbol%
     \fi
   \fi
   )}% Right bracket
\makeatother
\usetagform{bbrackets}

\begin{document}
\lipsum[5][2-3]

\begin{tabularx}{\textwidth}{@{}XX@{}}
\begin{equation}
f(x + y) = f(x) + f(y),
\label{eqn:1}
\end{equation} &
\begin{equation}
f(ax) = af(x),\,
x,y\in V, a\in\mathbb{C}
\label{eqn:2}
\end{equation}
\end{tabularx}

\lipsum[6][8-9]

\begin{tabularx}{\textwidth}{@{}XX@{}}
\begin{equation}
\overline{E}= -\overline \nabla \varphi-\frac{\partial \overline{A}}{\partial t}
\label{eqn:3}
\end{equation} &
\begin{equation}
\overline{B}=\overline \nabla \times\overline{A}\vphantom{-\frac{\partial \overline{A}}{\partial t}}
\label{eqn:4}
\end{equation}
\end{tabularx}
\end{document}