Is this a trick question? You made me think on this one. Do you see the smoke rising?
I was thinking that the batting is in the quilt so no need to cut it larger than the quilt backing.
Are you saying that you pre-wash batting? Now I see that in your post you are asking about cutting it before you pre-wash it...??
So I would pre-wash the whole piece of batting and then cut to size. Of course, I would over-size even that.
Geesh! I’m no help at all.
Would you please share how you pre-wash batting?