Centre alignment of table columns when setting column width

Question

I have a table as follows:

\begin{table} [H]
    \centering
    \setstretch{1.00}
    \begin{tabular}{R{1.00cm}p{3.50cm}p{3.5cm}p{2.50cm}p{2.00cm}}
    % \begin{tabular}{rcccc}
        \toprule        
        \multicolumn{1}{l}{\textbf{Num}} & \multicolumn{2}{c}{\textbf{Sentiment based upon}} & \multicolumn{1}{c}{\textbf{NER}} & \multicolumn{1}{l}{\textbf{Type}} \\
        \multicolumn{1}{l}{\textbf{}} & \multicolumn{1}{c}{\textbf{Human}} & \multicolumn{1}{c}{\textbf{Machine}} & \multicolumn{1}{l}{\textbf{}} \\        
        \midrule
        1 & \checkmark &          &            & Na\"{i}ve \\
        2 & &          \checkmark &            & Na\"{i}ve \\
        3 & &          \checkmark & \checkmark & Non-na\"{i}ve \\
        \bottomrule
    \end{tabular}
    \caption{Sentiment types.}
    \label{tab:SentimentTypes}
\end{table}

The second, third and fourth columns using checkmarks should be centre-aligned. But they insist on left-aligning instead as shown below:

Can anyone suggest why this is?