Currently, there are no ways, as far as I know, to control where a tag will be inserted when tagging an object. Revit will calculate the bounding box of the family and use the center of this bounding box to place the origin of the tag. This bounding box will include invisible graphics (eg. due to detail level) which creates unpredictable tag placements when building families with helper lines and similar features.
Please add a way to specify where the origin of a tag will be inserted. One way could be placing an object similar to the flip controls (but please make it snap for precise placement!) inside the family editor. If this object is not placed, use the default way of determining the insertion point.