Posição da figura no markdown ao converter para PDF com knitr e pandoc

Estou tentando controlar a posição de um gráfico ao converter para PDF usando knitr e pandoc. Meu arquivo .Rmd parece isto:

# My report

Some text some text some text some text some text some text some text some text some text


```{r myplot, echo=FALSE, fig.pos="placeHere", results='hide'}

library(ggplot2)

ggplot(mtcars, aes(mpg, drat)) + geom_point()

```

Some text some text some text some text some text some text some text some text some text

\usepackage{graphicx}
\begin{figure}[placeHere]
  \centering
    \includegraphics[width=0.5\textwidth]{placeHere}
\end{figure}

Some text some text some text some text some text some text some text some text some text

Estou convertendo para PDF usando as funções fornecidas aqui:http://quantifyingmemory.blogspot.co.uk/2013/02/reproducible-research-with-r-knitr.html

Como posso colocar o gráfico entre o segundo e o terceiro bloco de texto? O código de látex não está funcionando como está atualmente.

EDITAR: É isso que estou tentando agora.

# My report

   ```{r setup, include=FALSE}
# set global chunk options
opts_chunk$set(cache=FALSE)
library(ggplot2)
```

```{r, echo=FALSE, fig.height=3}

ggplot(mtcars, aes(disp, hp)) + geom_point()


```



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```{r, echo=FALSE, fig.height=3}



ggplot(mtcars, aes(vs, am)) + geom_point()


```



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```{r, echo=FALSE, fig.height=6}



ggplot(mtcars, aes(disp, cyl)) + geom_point()

```


```{r, echo=FALSE, fig.height=6}

ggplot(mtcars, aes(hp, qsec)) + geom_point()


```


Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some textSome text Some text Some text 




```{r, echo=FALSE, fig.height=3}

ggplot(mtcars, aes(hp, wt)) + geom_point()

```



Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some text Some textSome text Some text Some text 



```{r, echo=FALSE, fig.height=5}

ggplot(mtcars, aes(mpg, drat)) + geom_point()

```




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