Configuring subfigures within a tabular environment

I am trying to configure a table of subfigures (including multirow commands) within a tabular environment, however the result gives me an odd blank space above the mutlirow figure to the right. I have begun and ended the document with the appropriate userpackages. I have additional subfigures on the page before and after attached with the ContinuedFloat command. Any help with this would be amazing! Note that this is for a geological masters project for reference.

Code:

begin{figure}[h!]
centering
caption{Annotated stratigraphy at site RKBS9.}
label{fig:RKBS9_site}

begin{subfigure}{textwidth}
centering
includegraphics[width= linewidth]{Figures/Study_Site/Outcrops/RKBS9_slope_sq.pdf}
caption{Overview of site 9, indicating positions of detailed pictures.}
label{fig:RKBS9_slope}
end{subfigure}
end{figure}%
begin{figure}[ht]ContinuedFloat

centering
begin{tabular}{cc}
begin{subfigure}{0.45textwidth}
    centering
    includegraphics[width= linewidth]{Figures/Study_Site/Outcrops/RKBS9_top_sq2.pdf}
    caption{Upper cover-bed stratigraphy.}
    label{fig:RKBS9_top}
end{subfigure} 
& multirow{4}{*}{begin{subfigure}{0.45textwidth}
    centering
    includegraphics[width= linewidth]{Figures/Study_Site/Outcrops/RKBS9_out_sq2.pdf}
    caption{Contact between Breccas 2 and 1, with the interbedded Hinemaiaia Tephra.}
    label{fig:RKBS9_out}
end{subfigure}} 
begin{subfigure}{0.45textwidth}
    centering
    includegraphics[width= linewidth]{Figures/Study_Site/Outcrops/RKBS9_paleosol_sq2.pdf}
    caption{Paleosol separating Breccia 3 (upper) and Breccia 2 (lower).}
    label{fig:RKBS9_close}
end{subfigure}

end{tabular}
end{figure}%
begin{figure}[ht]ContinuedFloat
centering

begin{subfigure}{textwidth}
centering
includegraphics[width= linewidth]{Figures/Study_Site/Outcrops/RKBS9_longbomb.pdf}
caption{Detailed view of contact between Breccia 2 and 1, with a bomb sag indicting the violent 
impact ballistics preceding the deposition of Breccia 2.}
label{fig:RKBS9_longbomb}
end{subfigure}

end{figure}

The output of the subfigure table (excluding figures on other pages):

documentclass{article}
usepackage[vmargin=20mm]{geometry}
usepackage{multirow}
usepackage{subcaption}
usepackage[demo,  % in real document remove this option!
            export]{adjustbox}

begin{document}

begin{figure}[ht]
caption{Annotated stratigraphy at site RKBS9.}
label{fig:RKBS9_site}

begin{subfigure}{textwidth}
includegraphics[width=linewidth] {Figures/Study_Site/Outcrops/RKBS9_slope_sq.pdf}
caption{Overview of site 9, indicating positions of detailed pictures.}
label{fig:RKBS9_slope}
end{subfigure}
end{figure}

begin{figure}[ht]ContinuedFloat
centering
    begin{tabular}{cc}
begin{subfigure}[t]{0.45textwidth}
    centering
    includegraphics[width=linewidth, valign=t] {Figures/Study_Site/Outcrops/RKBS9_top_sq2.pdf}
    caption{Upper cover-bed stratigraphy.}
    label{fig:RKBS9_top}
end{subfigure} & multirow{4}{*}{begin{subfigure}{0.45textwidth}
    centering
    includegraphics[width=linewidth, height=1.1linewidth, valign=t] {Figures/Study_Site/Outcrops/RKBS9_out_sq2.pdf}
    % in real document remove `height` option or adjust to desired value
    caption{Contact between Breccas 2 and 1, with the interbedded Hinemaiaia Tephra.}
    label{fig:RKBS9_out}
end{subfigure}} 
%
begin{subfigure}{0.45textwidth}
    centering
    includegraphics[width= linewidth] {Figures/Study_Site/Outcrops/RKBS9_paleosol_sq2.pdf}
    caption{Paleosol separating Breccia 3 (upper) and Breccia 2 (lower).}
    label{fig:RKBS9_close}
end{subfigure}    &
    end{tabular}
end{figure}

begin{figure}[ht]ContinuedFloat
begin{subfigure}{textwidth}
centering
includegraphics[width= linewidth] {Figures/Study_Site/Outcrops/RKBS9_longbomb.pdf}
caption{Detailed view of contact between Breccia 2 and 1, with a bomb sag indicting the violent impact ballistics preceding the deposition of Breccia 2.}
label{fig:RKBS9_longbomb}
end{subfigure}

end{figure}
end{document}