From what I am experiencing, if you are using shared layers, the geometry of the object will be represented as 1:1 regardless of the unit ratio of the canvas.

E.g. I am designing mobile wireframes with canvases scaled at 1pt = 2px so they appear at approximately the 'real' size when printed. A box in a regular layer appears as 240x320, but that same box within a shared layer says 120x160, although they are visually identical.

IMO, scaling should be document-wide. It would certainly make painting by numbers easier!