Good news / bad news regarding your body.
The bad news is: you can’t change part of it — i.e. the thing you want to change — without affecting the whole thing.
That’s also the good news.
We talk about ourselves as if we’re parts — and from a certain perspective, this is true: psychologically, physically, emotionally. You do have a knee; you do have a shoulder.
And yet from a different, broader, perspective, there is only one thing happening, expressing as different things.
“Cranium goes left; pelvis and knees go right” is one way of thinking about a supine twist.
Knowing/feeling/imaging your one spine, expressing as its two different poles, is another way.
And so, by its very nature, to work with any bit is to work with all bits.
(So, also, you might as well start with what’s most obvious.)