Vertical alignment when rows are height-adjusted

[FloMiLe]

Starting with the example on page 20 of the manual, I set a specific row height:

\begin{tblr}{colspec={|X|X|X|X|X|X|}, rows = {30pt} } 
\hline 
Alpha & Beta & Gamma & Delta & Epsilon & Zeta \\
\hline 
\SetCell[r=2]{h} Eta & Theta & Iota & Kappa & Lambda & \SetCell[r=2]{m} Mu \\
\hline 
Nu & Xi & Omicron & Pi & Rho & Sigma \\
\hline 
\end{tblr}

But then I am not able to place Eta at the same vertical position as Theta and the rest of that row:

Is there a way to achieve this?

[muzimuzhi]

Maybe this doesn't work in general cases.

\documentclass{article}
\usepackage{tabularray}
\usepackage{xcolor}

% height of "normal" cells
%   @row-height = x + \abovesep + \ht\strutbox + \dp\strutbox + \belowsep + x
%   x = .5 * (@row-height - ...)
% required height of the first line in an h-aligned hspan cell
%   x + \abovesep + \ht\strutbox
% = .5 * (@row-height - ...) + \abovesep + \ht\strutbox
% = .5 * (@row-height + \abovesep + \ht\strutbox - \belowsep - \dp\strutbox)

\ExplSyntaxOn
\makeatletter
\def\yShiftForHspanCell{
  \rule{0pt}{
    .5\dimexpr
      % height of current row
      \__tblr_data_item:nen { row } { \the\c@rownum } { @row-height }
      + \abovesep + \ht\strutbox - \belowsep - \dp\strutbox
  }
}
\makeatother
\ExplSyntaxOff

\begin{document}
\begin{tblr}{hlines, vlines, colspec={*{6}{X}}, rows={30pt}}
  Alpha & Beta  & Gamma   & Delta & Epsilon & Zeta                 \\
  \SetCell[r=2]{h} Eta\yShiftForHspanCell
        & Theta & Iota\llap{\textcolor{blue}{\rule{5cm}{.2pt}}}
                          & Kappa & Lambda  & \SetCell[r=2]{m} Mu  \\
        & Xi    & Omicron & Pi    & Rho     &
\end{tblr}
\end{document}

[FloMiLe]

Thanks for your help and the solution!

So in this special case a low-level solution is required, and it's not like I missed some high-level setting...

Btw, a huge thank you for this awesome package that makes all other piece-meal packages for tables redundant (at least for me)!!!