The following figure is meant to be a contour graph. How can I extend the current shading out to the rest of the figure, so that there is shading between all of the lines?

Here is the the figure and the code.

[![enter image description here](https://i.stack.imgur.com/GihZa.png)](https://i.stack.imgur.com/GihZa.png)

```
\documentclass[tikz]{standalone}
\usetikzlibrary{angles}
\begin{document}
\begin{tikzpicture}
  \newcounter{cntShader}
  \setcounter{cntShader}{60}
  \coordinate (o) at (0,0);
  \draw[->] (o) -- (+80:4) coordinate (b);
  \draw[->] (o) -- (-80:4) coordinate (c);
  \draw (o) -- (+170:3);
  \draw (o) -- (-170:3);
  \foreach \rad in {3,2.5,...,.5} {
    \draw pic[draw,fill=gray!\thecntShader, angle radius=\rad cm] {angle=c--o--b};
    \pgfmathsetcounter{cntShader}{\thecntShader-10}
    \setcounter{cntShader}{\thecntShader}
    \draw (+80:\rad cm) -- +(+170:3cm);
    \draw (-80:\rad cm) -- +(-170:3cm);
  }
\end{tikzpicture}
\end{document}

```