Hi Dzonsi,
Sorry for the late reply, I've been a bit busy the last days.
When using the snippet-based technique, then the width and the height of the generated map is defined in the chosen template. You can inspect and change them in Plugin Manager -> MK_RNGMaps_withSnippets -> Templates.
When using the snippetless technique, then there's nothing to do. The generated map will have the same sizes as the space map itself.