According to R Markdown: The Definitive Guide, by default,
Plots emitted from a chunk are rendered to match the width of the editor at the time the chunk was executed. The height of the plot is determined by the golden ratio.
Specifying fig.size
would not change aspect ratio: you actually change the whole size of the picture (width and height are changed proportionally), but when RNotebook shows it to you it rescales it automatically to fit editor window. So you don't see a difference other than change of size of fonts, etc.
To actually produce taller image, you have to specify fig.asp
, like fig.asp=1.2
.
