Vertical alignment of \makecell header

Question

I have some issues with the vertical alignment of \makecell headers for a longtable. Basically, what I'm trying to achieve is that the single lettera A, B and E are vertically centered while the other cells remain at the bottom. I've increased the row height to show the effect.

MWE:

\documentclass[10pt]{scrbook}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{newpxtext}
    \linespread{1.05}
\usepackage[left=32.5mm, right=25mm, top=25mm, bottom=20mm]{geometry}
\usepackage{multirow}
\usepackage{makecell}
\usepackage{longtable}
\usepackage{ragged2e}
\newcolumntype{P}[1]{>{\RaggedRight\hspace{0pt}}p{#1}}
\newcolumntype{M}[1]{>{\centering}p{#1}}
\usepackage{pdflscape}
\newcommand{\rotl}{\rotatebox{90}}

\begin{document}

\begin{landscape}
    \setlength\tabcolsep{3.3pt}
    \renewcommand{\arraystretch}{1.3}
    \centering\footnotesize
    \begin{longtable}{|M{1.4cm}|M{1.4cm}|P{2.2cm}|P{1.5cm}|P{2cm}|M{0.4cm}|P{2cm}|M{0.4cm}|P{2cm}|M{0.4cm}|M{0.4cm}|P{2cm}|P{1.6cm}|P{1.5cm}|M{0.4cm}|M{0.4cm}|c|}
        \hline
        \multicolumn{2}{|c|}{} &  &  &  &  & \multicolumn{5}{c|}{IST Zustand} &  &  & \multicolumn{4}{c|}{optimierter Zustand} \\
        \cline{7-10} \cline{14-16}
        \multicolumn{2}{|c|}{\makecell[b]{Prozesselement/\\Funktion}} & \makecell[c]{mögliche Feheler} & \makecell[c]{Fehlerfolge} & \makecell[b]{Fehlerursache} & \makecell[c]{B} & \makecell[b]{Vermeidungs-\\maßnahme} & \makecell[c]{A} & \makecell[b]{Entdeckungs-\\maßnahme} & \makecell[c]{E} & \rotl{RPZ} & \multicolumn{1}{l|}{\makecell[b]{empfohlene\\Abstellmaßnahme}} & \makecell[b]{Verantwort-\\lich/Termin} & \makecell[b]{umgesetzte\\Maßnahme} & \makecell[t]{A} & E & \rotl{RPZ} \\[3mm]
        \hline
    \end{longtable}
\end{landscape}

\end{document}

Answer 1

You don't really need al this plethora of \makecells:

\documentclass[10pt, german]{scrbook}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{rotating}
\usepackage{newpxtext}
    \linespread{1.05}
\usepackage[left=32.5mm, right=25mm, top=25mm, bottom=20mm]{geometry}
\usepackage{multirow}
\usepackage{makecell}
\usepackage[column=O]{cellspace}
\setlength{\cellspacetoplimit}{4pt}
\setlength{\cellspacebottomlimit}{3pt}
\usepackage{longtable}
\usepackage{ragged2e}
\newcolumntype{P}[1]{>{\RaggedRight\hspace{0pt}}O{m{#1}}}
\newcolumntype{M}[1]{O{>{\centering}m{#1}}}
\usepackage{pdflscape}
\newcommand{\rotl}{\rotatebox[origin=c]{90}}
\newcommand{\nl}{\newline}

\begin{document}

\begin{landscape}
    \setlength\tabcolsep{3pt}
    \renewcommand{\arraystretch}{1.3}
    \centering\footnotesize%
    \begin{longtable}{|M{1.4cm}|M{1.4cm}|P{2.2cm}|P{1.5cm}|P{2cm}|M{0.4cm}|P{2cm}|M{0.4cm}|P{2cm}|M{0.4cm}|M{0.4cm}|P{2.3cm}|P{1.5cm}|P{1.5cm}|M{0.4cm}|M{0.4cm}|c|}
        \hline
        \multicolumn{2}{|c|}{} & & & & & \multicolumn{5}{c|}{IST Zustand} & & & \multicolumn{4}{c|}{optimierter Zustand} \\
        \cline{7-10} \cline{14-16}
        \multicolumn{2}{|c|}{\makecell{Prozesselement/\\Funktion}} & \nl mögliche Feheler & \nl Fehlerfolge & \nl Fehlerursache & B & Vermeidungs\-maßnahme & A & Entdeckungs\-maßnahme & E & \rotl{ RPZ} & \centering empfohlene\nl Abstellmaßnahme & Verantwort\-lich/Termin &umgesetzte\nl Maßnahm & A & E & \rotl{RPZ} \\
        \hline
    \end{longtable}
\end{landscape}

\end{document}