Another small comment: can you conform the explanation of the new parameter to the [numpy docstring standard](https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt#sections)? This is:

```
param : type
    Description of parameter `param`.
```
I know that all the other parameters in this function also don't follow this, but I think trying to do it for new code is a good start.

So here, I suppose this would look like this:
```
xy_range_extension : float, default 0.05
    percentage ...
```