Question about __expand_window()

Hi!

Thank you for developing and sharing this library. I have been using it quite successfully.

In function `__expand_window()`, is there a reason for _thickening_ the path with `radius` **before** doubling the search window axes rather than the other way around? 
This way the search window becomes `4 * radius` instead of `2 * radius`. 

Thanks in advance,
Vasco.