How to reduce top margin of chapter title page?

Question

I need 1in top margin in all pages. Chapter title page taking more margin that i need.

This is my MWE:

\documentclass[a4paper,12pt]{report}
\usepackage[left=1.5in,right=1in,top=1in,bottom=1in,includefoot,heightrounded]{geometry}
\usepackage{lipsum}
\renewcommand{\baselinestretch}{1.3}
\usepackage[pagestyles]{titlesec}
\newpagestyle{mine}{%
\headrule
\sethead{\itshape\chaptername\thechapter}{}{\itshape\chaptertitle}
\setfoot{}{}{\thepage}}%

\renewpagestyle{plain}{%
\setfoot{}{}{\thepage}}%

\titleformat{\chapter}[display]{\normalfont\huge\bfseries\centering}   {\chaptertitlename\ \thechapter}{20pt}{\Huge}
\titlespacing{\chapter}{0pt}{0pt}{1cm}
\pagenumbering{roman}
\pagestyle{mine}
\begin{document}
\chapter*{Abstract}
\lipsum[2-4]
\chapter{Introduction}

\pagenumbering{arabic}
\setcounter{page}{1}
\lipsum[2-10]

\end{document} 

Please tell me how can i achive that?

Answer 1

I just changed the \titlespacing parameter #3 to -32pt.

\documentclass[a4paper,12pt]{report}

\usepackage[showframe,left=1.5in,right=1in,top=1in,bottom=1in,includefoot,heightrounded]{geometry}
\usepackage{lipsum}
\renewcommand{\baselinestretch}{1.3}
\usepackage[pagestyles]{titlesec}
\newpagestyle{mine}{%
\headrule
\sethead{\itshape\chaptername\thechapter}{}{\itshape\chaptertitle}
\setfoot{}{}{\thepage}}%

\renewpagestyle{plain}{%
\setfoot{}{}{\thepage}}%

\titleformat{\chapter}[display]{\normalfont\huge\bfseries\centering}   {\chaptertitlename\ \thechapter}{20pt}{\Huge}
\titlespacing{\chapter}{0pt}{-32pt}{1cm}% <-- CHANGE DONE HERE!!
\pagenumbering{roman}
\pagestyle{mine}


\begin{document}
\chapter*{Abstract}

\lipsum[2-4]
\chapter{Introduction}

\pagenumbering{arabic}
\setcounter{page}{1}
\lipsum[2-10]

\end{document}