New line size. What can I do?

Question

I'm writing my Ph.D. thesis and I'm using a format that a colleague of mine gave me. I noticed a strange situation: there are all around blocks of text that I separate with \\ only. Anyway, on pdf output, I get that some newline are larger than others.

For example, this one has a normal newline:

...individuals' satisfaction degree. \\

A pioneering and well-known model depicting such situation...

while this other one has a very large newline (wrong or unwanted behavior):

...even though they have been conceived in different ways.\\

Even though there is a plenty of works studying ...

These two newlines are defined in the same ways. The code you see is exactly a copy-and-paste from my tex. I don't know where to start in order to understand what I'm doing wrongly.

Addition 1 Hereafter you find the master tex file:

\documentclass[12pt,makeidx]{phdthesis}

\usepackage{a4wide}
\usepackage{appendix}
\usepackage{cite}

\usepackage{avant}

\usepackage{makeidx}  
\makeindex


\usepackage[english]{babel}
\usepackage{fancyheadings}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{amstext}
\usepackage{amsmath}    
\usepackage{graphicx}   
\usepackage{amsthm}
\usepackage{xcolor}
\usepackage{hyperref}
\usepackage{enumitem}



%%% General page formatting %%%%
\addtolength{\textwidth}{-0.6in} %-0.6
\addtolength{\evensidemargin}{0.3in} %0.3
\addtolength{\oddsidemargin}{0.3in} %0.3

%\addtolength{\topmargin}{1.00in}
%\addtolength{\textheight}{2.00in}

\renewcommand{\textfraction}{0.01}
\renewcommand{\topfraction}{0.99}
\renewcommand{\floatpagefraction}{0.99}
\renewcommand{\bottomfraction}{0.99}
\renewcommand{\baselinestretch}{1.2} 


\newcommand{\Complex}{\mathbb{C}}
\newcommand{\Real}{\mathbb{R}}
\newcommand{\Integer}{\mathbb{Z}}
\newcommand{\Natural}{\mathbb{N}}
\newcommand{\Endproof}{$\hfill\square$}
\newcommand{\needcite}{{\color{red}[\textbf{Citation needed}]}}
\newcommand{\bs}[1]{\boldsymbol{#1}}
\newcommand{\todo}[1]{{\color{red}[\textbf{TODO: }#1]}}
\newcommand{\edited}{\color{MidnightBlue}}


\newtheorem{Theorem}{Theorem}
\newtheorem{Corollary}{Corollary}

\begin{document}
\pagestyle{fancyplain}
\pagenumbering{roman}


%% create the table of contents
\cleardoublepage
\lhead[]{\fancyplain{}{\rightmark}}
\chead[\fancyplain{}{}]{\fancyplain{}{}}
\rhead[\fancyplain{}{\leftmark}]{\fancyplain{}{}}
%\rhead[\fancyplain{}{}]{\fancyplain{}{}}
%\lhead[\fancyplain{}{}]{\fancyplain{}{}}
\begin{center}
{\huge My thesis}
\end{center}

\tableofcontents
\include{src/lop} % list of publications of author
\cleardoublepage

\newcommand{\publ}{}

\pagestyle{fancyplain}
%\setlength{\headrulewidth}{0.3pt}
%\setlength{\footrulewidth}{0.0pt}
%\setlength{\plainfootrulewidth}{0.0pt}
%\setlength{\plainheadrulewidth}{0pt}
\renewcommand{\sectionmark}[1]{\markright{\it \thesection.\ #1}}
\renewcommand{\chaptermark}[1]{\markboth{\it \thechapter.\ #1}{}}
\lhead[\thepage]{\fancyplain{\publ}{\rightmark}}
\chead[\fancyplain{}{}]{\fancyplain{}{}}
\rhead[\fancyplain{}{\leftmark}]{\fancyplain{}{\thepage}}
\lfoot[]{} \cfoot[]{} \rfoot[]{}
%------------------------------


\include{src/intro}
\include{src/game/game}
%\include{src/eeg} 
%\include{src/bio/bio} 


%% Include the bibliography
%\renewcommand{\publ}{}
\cleardoublepage
\small
\addcontentsline{toc}{chapter}{Bibliografy}
%\bibliography{Biblio_PhDThesis}
\include{src/biblio}

%% Include the index
\cleardoublepage
\addcontentsline{toc}{chapter}{Index}
\printindex

\end{document}

Answer 1

Never end a paragraph with \\ it forces a line break after the last word of the paragraph producing an empty line that messes up the space and produces

Underfull \hbox (badness 10000) in paragraph at lines...

in the log. Note that 10000 is infinitely bad. TeX is telling you that the spacing in this document has been forced to be as bad as it measures.

If you have large unbreakable boxes in your text you may prefer \raggedbottom rather than \flushbottom where TeX tries to keep the baseline of the bottom row of each page at the same point, so may have to stretch white space to achieve that, but without an example it is hard to be sure. But first you need to remove the \\ commands as it is impossible to get correct spacing with that markup.