XeLaTeX: Shift baseline of Tibetan font

Question

I had a look at different approaches discussed on SO, but they either don't apply to the Tibetan font (e.g. only CJK fonts) or they lower the whole line (not just the part inside the curly braces) or they involve a block which prevents automatic line breaks from working (like \raisebox).

Any idea how I can lower the baseline of the Tibetan font (BabelStrone Tibetan) to make it align with the English text around it?

\documentclass{article}

\usepackage{polyglossia}
\setdefaultlanguage[variant=british]{english}
\setotherlanguage{tibetan}
\setmainfont{Charis SIL}
\newfontfamily{\tibetanfont}[Scale=1.415]{BabelStone Tibetan}

\setlength{\parindent}{0pt}

\begin{document}
the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’\\
\end{document}

I want to make it look like in the second line in the image below where I'm using a different Tibetan font that has better vertical alignment.

Answer 1

Using this answer, you can adjust the baseline with a PDF special.

Update to allow for difference font sizes.

\documentclass{article}

\usepackage{polyglossia}
\setdefaultlanguage[variant=british]{english}
\setotherlanguage{tibetan}
\setmainfont{Charis SIL}
\newfontfamily{\tibetanfont}[Scale=1.415]{BabelStone Tibetan}

\setlength{\parindent}{0pt}

\usepackage{xparse}
\ExplSyntaxOn
\dim_new:N \g__naoki_offset_dim
\cs_new:Nn \__naoki_calc_offset:
  {
    \dim_set:Nn \g__naoki_offset_dim { 1 ex * \dim_ratio:nn { 2 pt } { 5 pt } }
  }
\NewDocumentCommand \dropbaseline { }
  {
    \__naoki_calc_offset:
    \special{pdf:literal~1~0~0~1~0~-\dim_to_decimal:n { \g__naoki_offset_dim }~cm}
  }
\NewDocumentCommand \raisebaseline { }
  {
    \__naoki_calc_offset:
    \special{pdf:literal~1~0~0~1~0~\dim_to_decimal:n { \g__naoki_offset_dim }~cm}
  }
\ExplSyntaxOff

\usepackage{xpatch}
\xpretocmd{\texttibetan}{\dropbaseline}{}{}
\xapptocmd{\texttibetan}{\raisebaseline}{}{}

\newlength{\tempdima}
\begin{document}
English {\tibetanfont\dropbaseline རྫོང་\raisebaseline} English

\Huge the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’

\huge the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’

\LARGE the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’

\Large the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’

\large the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’

\normalsize the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’

\small the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’

\footnotesize the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’

\scriptsize the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’

\tiny the \texttibetan{རྫོང་} \textbf{dzong} ‘fortress’
\end{document}