How to make the interactive area(move,scale,rotate) of Scatter widget cover the left and below of child widget in Kivy?

Question

1, My question

When using Scatter widget to add some child widget(like label/image), how to make the interactive area(move/rotate/scale) of Scatter not just limited by the initial size of window？Because this will make the areas to the left and below the child widget(button k in my case) to be undraggable.

2, Example

current situation

from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.scatter import Scatter

class Xapp(App):
    def build(self):
        ss=Scatter()

        k=Button(text='this is a k',font_size=30)
        k.size=(200,100)
        ss.add_widget(k)

        return ss

Xapp().run()

3, What I want to achieve

interactive area to be wrap around or cover button k

Ideally, the interactive area of Scatter should be infinitely large, as if button k were a pattern on the Photoshop layer(like illustration-E). If that's not possible, is it possible to align the center of the button with the center of the interactive area of scatter? (like illustration-D)