For a Boss feature, the curves of the Boss are offset and then clipped against the shape of the stock. When using a square piece of stock the toolpaths tend to cut the four corners first, and then work their way inward. You can alter the extent of the toolpaths by using a stock curve of total stock.
For a Pocket feature, the boundary of the Pocket is offset and the toolpaths are cut starting from the center of the pocket. The shape of the stock does not affect the toolpaths.
