tweaking the positioning of tikz arrows (such as on a curved path)

Question

I believe that this is a duplicate of a question/answer posted within the past two months. But, after much searching, I still can't find it. Does someone out there know the link?

My question

I'm not happy with the placement of the arrow in the following picture. Anyone know how to correct the angle at which the arrow is attached to the arc?

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\pagestyle{empty}
\setlength{\parindent}{0pt}
\begin{document}

\begin{tikzpicture}[x=0.5cm,y=0.5cm]
    \draw[help lines,blue!20,step=1] (0,0) grid (12,12);

    \draw[fill]  (0,0) coordinate [label=180:Z] (Z) circle (2pt);           %% center of the picture
    \draw[fill]  (5,5) coordinate [label=135:Q] (Q) circle (2pt);           %% center of the circle
    \draw[fill]  (Q) -- +(  0:6)   coordinate [label=0:A] (A) circle (2pt); %% first point on the circle
    %% drawing the circle
    \draw[blue]  (A) 
                 let \p1 = ($ (A) - (Q) $) in
                 arc(0:360:{veclen(\x1,\y1)});

    %% PROBLEMATIC LINES
    \draw [line width=0.4pt,red]
          let \p1 = ($(A) - (Q)$), \n1={veclen(\x1,\y1)} in
          (Q) -- +(320:\n1)
          coordinate (B) circle (2pt);




    \draw[purple,line width=0.4pt] 
          (B) -- +($  (0,0) ! 2em ! 0 : ($(B)-(Q)$)  $)  
          coordinate [label=center:B] (Bl) circle (6pt);

    \draw[blue]   
          ($ (B) ! 0.45 ! (Q) $) 
          coordinate (tC) circle (2pt);

    \draw[line width=1.5em,->]
          (tC) 
          let \p1 = ($(tC) - (Q)$) in
              arc ({atan2(\x1,\y1)}:{atan2(\x1,\y1)+90}:{veclen(\x1,\y1)});

\end{tikzpicture}

\end{document}

UPDATE

OK, the link was found at Create curved TikZ single arrow, but I'm still having difficulty getting it to work. Here's one example of what I've tried.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\pagestyle{empty}
\setlength{\parindent}{0pt}
\begin{document}

\begin{tikzpicture}[x=0.5cm,y=0.5cm]
    \draw[help lines,blue!20,step=1] (0,0) grid (12,12);

    \draw[fill]  (0,0) coordinate [label=180:Z] (Z) circle (2pt);           %% center of the picture
    \draw[fill]  (5,5) coordinate [label=135:Q] (Q) circle (2pt);           %% center of the circle
    \draw[fill]  (Q) -- +(  0:6)   coordinate [label=0:A] (A) circle (2pt); %% first point on the circle
    %% drawing the circle
    \draw[blue]  (A) 
                 let \p1 = ($ (A) - (Q) $) in
                 arc(0:360:{veclen(\x1,\y1)});

    %% PROBLEMATIC LINES
    \draw [line width=0.4pt,red]
          let \p1 = ($(A) - (Q)$), \n1={veclen(\x1,\y1)} in
          (Q) -- +(320:\n1)
          coordinate (B) circle (2pt);

    \draw[purple,line width=0.4pt] 
          (B) -- +($  (0,0) ! 2em ! 0 : ($(B)-(Q)$)  $)  
          coordinate [label=center:B] (Bl) circle (6pt);

    \draw[blue]   
          ($ (B) ! 0.45 ! (Q) $) 
          coordinate (tC) circle (2pt);

    \draw[line width=01.5em,->,end angle=230]
          (tC) 
          let \p1 = ($(tC) - (Q)$), 
              \n1={atan2(\x1,\y1)}, %% start angle
              \n2={\n1+90},         %% end angle
              \n3={veclen(\x1,\y1)} %% radius
          in
              arc (\n1:\n2:\n3)
              -- ++(\n2+90:\n3)
          %    -- ++(\n2+0:\n3)
             ;

\end{tikzpicture}

\end{document}

But there's a bit more length to the arrow than I want.

A bit more hacking seems to get it

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\pagestyle{empty}
\setlength{\parindent}{0pt}
\begin{document}

\begin{tikzpicture}[x=0.5cm,y=0.5cm]
    \draw[help lines,blue!20,step=1] (0,0) grid (12,12);

    \draw[fill]  (0,0) coordinate [label=180:Z] (Z) circle (2pt);           %% center of the picture
    \draw[fill]  (5,5) coordinate [label=135:Q] (Q) circle (2pt);           %% center of the circle
    \draw[fill]  (Q) -- +(  0:6)   coordinate [label=0:A] (A) circle (2pt); %% first point on the circle
    %% drawing the circle
    \draw[blue]  (A) 
                 let \p1 = ($ (A) - (Q) $) in
                 arc(0:360:{veclen(\x1,\y1)});

    %% PROBLEMATIC LINES
    \draw [line width=0.4pt,red]
          let \p1 = ($(A) - (Q)$), \n1={veclen(\x1,\y1)} in
          (Q) -- +(320:\n1)
          coordinate (B) circle (2pt);

    \draw[purple,line width=0.4pt] 
          (B) -- +($  (0,0) ! 2em ! 0 : ($(B)-(Q)$)  $)  
          coordinate [label=center:B] (Bl) circle (6pt);

    \draw[blue]   
          ($ (B) ! 0.45 ! (Q) $) 
          coordinate (tC) circle (2pt);

    \draw[line width=01.5em,->]
          (tC) 
          let \p1 = ($(tC) - (Q)$), 
              \n1={atan2(\x1,\y1)}, %% start angle
              \n2={\n1+90},         %% end angle
              \n3={veclen(\x1,\y1)} %% radius
          in
              arc (\n1:\n2:\n3)
              -- ++(\n2+80:1em)
             ;

\end{tikzpicture}

\end{document}