A good Sissy should always be accessible and waist height is pretty much where she belongs no matter which way you look at it!
Why do you call this bending at the waist? As the image shows, the bend has to happen at the hips - and preferably with straight knees - for it to serve its purpose. Bending at the waist is for butlers.
You know what? I stand corrected. I do believe you are correct.
Waist or hips? It shouldn't matter how you describe it as long as it's properly performed. Wouldn't you agree!