I agree with tyflier, you can rotate the top 3 sections if you want to. It is not crucial that the spine aligns with the spine of the butt section [if you can even locate it]. like you said the butt doesn't flex much any way.
As far as putting them on the spine or opposite I've never really noticed much of a differance. But they DO have to be either on the spine or 180 degrees opposite.

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To fish or not to fish?
What a stupid question.