Inkscape

The ”Filter General Settings” has four spinboxes where you can type in values.
The ”Coordinates” row sets the (x,y) position of the top left corner of the filtered area relative to the object's original bounding box, while the
”Dimensions” row sets the width and height, relative to the original bounding box.

That is a fairly important part as effects that go over the original boundaries may gat chopped off at a filtered area set too small.
If the effect is used to generate a texture to the object, the default values are usually fine.
Those invoke the filtered area 1,2 (or 120%) times larger than the original, centered to the object.