Acoustic Guitar Construction

I am finding it difficult to understand where the MM center spindle gets to be located. Is it always dead-center of the guitar body? If not, I'd love to pick up enough insight so's I can determine that. Right now I'm making three 'shrunken' dreadnought bodies, so once the location is known, it can hang around for a while.

Thanks very much.

Length mid-point

Thanks, Ken. Upon reflection, seeing as we're trying to make the back a slice off a sphere, that makes sense.

Much obliged.