# single table cell out of vertical alignment

Having been guided by the wisdom of those more experienced than me, I have been using this answer to my previous question to change all my tables into ones that look better using booktabs. One of my tables is giving me some grief. The vertical alignment of one of my header row cells is off, and I have no idea why.

\documentclass[12pt, a4paper, oneside, fleqn]{report}
\usepackage{geometry}
\geometry{
top=2.5cm,
left=3.5cm,
bottom=2.5cm,
right=2.5cm,
showframe,
}

\usepackage{array,booktabs}

\renewcommand{\arraystretch}{1.5}
\newcolumntype{L}[1]{>{\raggedright\let\newline\\\arraybackslash\hspace{0pt}}p{#1}}
\newcolumntype{C}[1]{>{\centering\let\newline\\\arraybackslash\hspace{0pt}}p{#1}}
\newcolumntype{R}[1]{>{\raggedleft\let\newline\\\arraybackslash\hspace{0pt}}p{#1}}

\bfseries
\begin{tabular}{@{}c@{}}
\strut#1\strut
\end{tabular}%
}

\begin{document}

\begin{table}
\footnotesize
\centering
\begin{tabular}[t]{ l L{5cm} L{3cm} L{3.5cm} }
\toprule
\midrule
IASI  & Infrared Atmospheric Sounding Interferometer & IR interferometer & Atmospheric temperature and humidity profiles; trace gases \\
AMSU  & Advanced Microwave Sounding Unit & Microwave radiometer & Atmospheric temperature \\
MHS   & Microwave Humidity Sounder       & Microwave radiometer & Atmospheric humidity    \\

\bottomrule
\end{tabular}
\caption{My table of instruments}
\end{table}

\end{document}


Gives the following output. Why is the middle one bottom aligned?