Poor subfigure and subcaption alignment

Question

I have the following figure, containing three subfigures:

I'm using the following code to produce it/them:

\begin{figure}[htbp]%
\tikzstyle{morpho} = [circle,draw,minimum size=1cm,thick,fill=white,font=\tiny]%
\tikzstyle{grouping} = [thick,rounded corners=5pt,fill=#1!20]%
\pgfmathsetmacro{\O}{0.6}%
\pgfmathsetmacro{\P}{1.5}%
\centering
\begin{subfigure}[b]{0.3\textwidth}
\centering
\begin{tikzpicture}
\coordinate (A)  at (0,0);
\coordinate (O)  at (\P,0);
\coordinate (Sa) at (0,-\P);
\coordinate (Ss) at (\P,-\P);
\draw[grouping=blue]
    ($(A)+(-\O,\O)$) --($(A)+(\O,\O)$)  -- ($(Sa)+(\O,\O)$) --
    ($(Ss)+(\O,\O)$) -- ($(Ss)+(\O,-\O)$) -- ($(Sa)+(-\O,-\O)$) -- cycle;
\draw[grouping=red]
    ($(O)+(-\O,\O)$) -- ($(O)+(\O,\O)$) -- ($(O)+(\O,-\O)$) -- ($(O)+(-\O,-\O)$) -- cycle;
\node[morpho] at (A)  {Agent};
\node[morpho] at (O)  {Patient};
\node[morpho] at (Sa) {Active};
\node[morpho] at (Ss) {Stative};
\end{tikzpicture}
\caption{Nominative-Accusative}
\end{subfigure}
\begin{subfigure}[b]{0.3\textwidth}
\centering
\begin{tikzpicture}
\coordinate (A)  at (0,0);
\coordinate (O)  at (\P,0);
\coordinate (Sa) at (0,-\P);
\coordinate (Ss) at (\P,-\P);
\draw[grouping=red]
    ($(O)+(-\O,\O)$) --($(O)+(\O,\O)$)  -- ($(Ss)+(\O,-\O)$) --
    ($(Sa)+(-\O,-\O)$) -- ($(Sa)+(-\O,\O)$) -- ($(Ss)+(-\O,\O)$) -- cycle;
\draw[grouping=blue]
    ($(A)+(-\O,\O)$) -- ($(A)+(\O,\O)$) -- ($(A)+(\O,-\O)$) -- ($(A)+(-\O,-\O)$) -- cycle;
\node[morpho] at (A)  {Agent};
\node[morpho] at (O)  {Patient};
\node[morpho] at (Sa) {Active};
\node[morpho] at (Ss) {Stative};
\end{tikzpicture}
\caption{Ergative-Absolutive}
\end{subfigure}
\begin{subfigure}[b]{0.3\textwidth}%
\centering
\begin{tikzpicture}
\coordinate (A)  at (0,0);
\coordinate (O)  at (\P,0);
\coordinate (Sa) at (0,-\P);
\coordinate (Ss) at (\P,-\P);
\draw[grouping=red]
    ($(O)+(-\O,\O)$) -- ($(O)+(\O,\O)$) -- ($(O)+(\O,-\O)$) -- ($(O)+(-\O,-\O)$) -- cycle;
\draw[grouping=blue]
    ($(A)+(-\O,\O)$) -- ($(A)+(\O,\O)$) -- ($(A)+(\O,-\O)$) -- ($(A)+(-\O,-\O)$) -- cycle;
\draw[grouping=green]
    ($(Sa)+(-\O,\O)$) --($(Ss)+(\O,\O)$)  -- ($(Ss)+(\O,-\O)$) -- ($(Sa)+(-\O,-\O)$) -- cycle;
\node[morpho] at (A)  {Agent};
\node[morpho] at (O)  {Patient};
\node[morpho] at (Sa) {Active};
\node[morpho] at (Ss) {Stative};
\end{tikzpicture}
\caption{Ergative-Accusative (Tripartite)}
\end{subfigure}
\caption{Morphosyntactic Alignments}
\end{figure}

There are several obvious problems with this. One, the tops of the drawings are not aligned (it looks like LaTeX is aligning to the bottom of the captions). Second, the captions themselves look really ugly. For figure 5.1a, there's the leading space in front of "Nominative-". For figure 5.1c, I think the layout of the text doesn't look very good. Instead of

(c)   Ergative-Accusative
(Tripartite)

I would prefer something like

(c)   Ergative-Accusative
      (Tripartite)

Update:

So thanks to a commenter, I was able to figure out the alignment problem: I had forgotten about the "b" option left in from an example I had originally copy/pasted. Here's what my output looks like now:

I increased the width of each of the subfigures from 0.3 to 0.32 of the textwidth, so there's no line breaking anymore for "Nominative-Accusative." However, I still have the problem with 5.1c. It has the leading space, which looks bad, and I can't figure out how to get it to align as mentioned earlier. I should also mention that I'm using the subcaption package.

Answer 1

Let me convert my comment to an answer:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{ragged2e}% <-- added package
\usepackage[justification=RaggedRight,
            format=hang]{subcaption}% <-- definition of the subcaption format 

\begin{document}
    \begin{figure}
\tikzset{% <-- \tikzstyle is replaced by \tikzset
  morpho/.style = {circle,draw,thick,
                   fill=white,minimum size=1cm,
                   inner sep=2pt,% <-- changed inner sep
                   font=\scriptsize},% <-- changed font size
grouping/.style = {thick,rounded corners=5pt,fill=#1!20}
        }
\pgfmathsetmacro{\O}{0.6}%
\pgfmathsetmacro{\P}{1.5}%

\begin{subfigure}[t]{0.32\textwidth}% <--- increased size of subfigure
\centering
\begin{tikzpicture}
\coordinate (A)  at (0,0);
\coordinate (O)  at (\P,0);
\coordinate (Sa) at (0,-\P);
\coordinate (Ss) at (\P,-\P);
\draw[grouping=blue]
    ($(A)+(-\O,\O)$) --($(A)+(\O,\O)$)  -- ($(Sa)+(\O,\O)$) --
    ($(Ss)+(\O,\O)$) -- ($(Ss)+(\O,-\O)$) -- ($(Sa)+(-\O,-\O)$) -- cycle;
\draw[grouping=red]
    ($(O)+(-\O,\O)$) -- ($(O)+(\O,\O)$) -- ($(O)+(\O,-\O)$) -- ($(O)+(-\O,-\O)$) -- cycle;
\node[morpho] at (A)  {Agent};
\node[morpho] at (O)  {Patient};
\node[morpho] at (Sa) {Active};
\node[morpho] at (Ss) {Stative};
\end{tikzpicture}
    \caption{Nominative-Accusative}
\end{subfigure}
\hfill
\begin{subfigure}[t]{0.32\textwidth}% <--- increased size of subfigure
\centering
\begin{tikzpicture}
\coordinate (A)  at (0,0);
\coordinate (O)  at (\P,0);
\coordinate (Sa) at (0,-\P);
\coordinate (Ss) at (\P,-\P);
\draw[grouping=red]
    ($(O)+(-\O,\O)$) --($(O)+(\O,\O)$)  -- ($(Ss)+(\O,-\O)$) --
    ($(Sa)+(-\O,-\O)$) -- ($(Sa)+(-\O,\O)$) -- ($(Ss)+(-\O,\O)$) -- cycle;
\draw[grouping=blue]
    ($(A)+(-\O,\O)$) -- ($(A)+(\O,\O)$) -- ($(A)+(\O,-\O)$) -- ($(A)+(-\O,-\O)$) -- cycle;
\node[morpho] at (A)  {Agent};
\node[morpho] at (O)  {Patient};
\node[morpho] at (Sa) {Active};
\node[morpho] at (Ss) {Stative};
\end{tikzpicture}
\caption{Ergative-Absolutive}
\end{subfigure}
\hfill
\begin{subfigure}[t]{0.32\textwidth}% <--- increased size of subfigure
\centering
\begin{tikzpicture}
\coordinate (A)  at (0,0);
\coordinate (O)  at (\P,0);
\coordinate (Sa) at (0,-\P);
\coordinate (Ss) at (\P,-\P);
\draw[grouping=red]
    ($(O)+(-\O,\O)$) -- ($(O)+(\O,\O)$) -- ($(O)+(\O,-\O)$) -- ($(O)+(-\O,-\O)$) -- cycle;
\draw[grouping=blue]
    ($(A)+(-\O,\O)$) -- ($(A)+(\O,\O)$) -- ($(A)+(\O,-\O)$) -- ($(A)+(-\O,-\O)$) -- cycle;
\draw[grouping=green]
    ($(Sa)+(-\O,\O)$) --($(Ss)+(\O,\O)$)  -- ($(Ss)+(\O,-\O)$) -- ($(Sa)+(-\O,-\O)$) -- cycle;
\node[morpho] at (A)  {Agent};
\node[morpho] at (O)  {Patient};
\node[morpho] at (Sa) {Active};
\node[morpho] at (Ss) {Stative};
\end{tikzpicture}
\caption{Ergative-Accusative (Tripartite)}
\end{subfigure}
\caption{Morphosyntactic Alignments}
    \end{figure}
\end{document}

Above MWE gives:

The formatting of main caption is left to default settings defined in article document class. It can be changed with caption package.