Equal spacing only between some columns of a table

Question

I am trying to make this table look nicer, I've tried the >{\hsize=.85\hsize} trick, but can't get it last part to be short. I am almost sure there is more elegant solution. Basically I need the last three columns to be equally spaced and almost-same-size.

(arbitrary margin just to match my institution requirements without loading custom packages) MWE:

\documentclass[,a4paper]{memoir}
\usepackage[adobe-utopia]{mathdesign}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{tabularx}
\usepackage{threeparttable}
\usepackage{booktabs}
\usepackage[margin=3.8cm]{geometry}
%***********************Document*******************
\begin{document}
    \begin{threeparttable}{\small 
            \linespread{1.3}\selectfont{}
            \begin{tabularx}{\textwidth}{@{}XXXX@{}}\toprule
                Factor & Low & Medium & High\\
                \midrule
                Physiochemical & & &\\ 
                \hspace{1em}Smothing abc.\ & Molecular flow & Molecular flow & Continuum flow \\ 
                \hspace{1em}Sticking coef.\ & Reversible adsorption & Adsorption & High eff.\ adsorption\\ 
                \hspace{1em}Available mol.\ & Insufficient coverage & Surface saturation & {Precursor waste \tnote{$\dagger$}}\\
                \addlinespace[1ex] %\hdashline
                \midrule
                Processing &  &  & \\ 
                %\cmidrule(){1-1}
                \hspace{1em}{Temperature} & {Condensation} & {Adsorption} & {Desorption \tnote{$\star$}}\\ 
                \hspace{1em}Pressure & Poor precursor carrier & Balanced & Lower interdiffusion\\ 
                \hspace{1em}Exposure time & Insufficient coverage & Complete coverage & Longer cycle\\
            \bottomrule
    \end{tabularx}}

    \begin{tablenotes}
        \item[$\dagger$] Another thing.
        \item[$\star$] Something.
        \item Source: BBQ.
    \end{tablenotes}
\end{threeparttable}

\end{document}

Desired result like this:

I have read through a lot of questions, specially this and this other one. Most questions seem to related either to, multicolumn, long table, or number-content tables, which is not my case.

Answer 1

Based on the annotated screenshot you posted, it looks like you want equal amounts of whitespace between the columns and no whitespace to the right of the final column. A tabular* environment lets you achieve these formatting objectives.

\documentclass[a4paper]{memoir}
\usepackage[adobe-utopia]{mathdesign}
%%\usepackage[utf8]{inputenc} % that's the default nowadays
\usepackage[T1]{fontenc}
\usepackage{array}
\newcommand\mc[1]{\multicolumn{1}{@{}l}{#1}} % handy shortcut macro
\usepackage[flushleft]{threeparttable}
\usepackage{booktabs}
\usepackage[margin=3.8cm]{geometry}
\begin{document}
\noindent
\begin{threeparttable} 
%% \small % not needed
\setlength\tabcolsep{0pt} % default: 6pt
\linespread{1.15} % "\linespread{1.3}" seems excessive
\begin{tabular}{\textwidth}{@{\extracolsep{\fill}} >{\quad}l lll }
\toprule
     \mc{Factor} & Low & Medium & High\
     \midrule
     \mc{Physiochemical} \ 
     Smoothing abc.\ & Molecular flow & Molecular flow & Continuum flow \ 
     Sticking coeff.\ & Reversible adsorption & Adsorption & High eff.\ adsorption\ 
     Available mol.\ & Insufficient coverage & Surface saturation & Precursor waste\tnote{$\dagger$} \
     \midrule
     \mc{Processing} \ 
     Temperature & Condensation & Adsorption & Desorption\tnote{$\star$}\ 
     Pressure & Poor precursor carrier & Balanced & Lower interdiffusion\ 
     Exposure time & Insufficient coverage & Complete coverage & Longer cycle\
\bottomrule
\end{tabular}
\smallskip

\footnotesize
\begin{tablenotes}
   \item[$\dagger$] Another thing.
   \item[$\star$] Something.
   \item[\phantom{$\dagger$}] Source: BBQ.
\end{tablenotes}
\end{threeparttable}
\end{document}