Graphics

I'm trying to use the height of a group's bounding box to move it down one position.  However, the height is greater then the height of any of the object's with in the group.  

I have a 4 groups lined up vertically and want to be able to switch the order.  I am trying to do that by the height of the bounding box.  If it is moved down the list then I change the y position as follows:

PosY = PosY - bounding box height.

however, in my case, the maximum height of any object in the group is 30 (and all of the pivots are lined up and the y values are all 0) but the height shows as 61, 91, etc for the bounding boxes.  

What sets the height of the bounding box for a group?

I have an additional question in relation to this.  How is the bounding box defined for a group?  For an object with an image it makes sense that the bounding box is the dimension set for the size of the image.  

What I am seeing.  If I put the position of the group at y = 0 the bounding box height is 30 (the height of the largest object inside the group.  If I put the position at a positive value I appear to get the same.  However, if I put the position of the group below the x axis (i.e. -ve) it will give me an odd result. For example y= -50, largest object height 30 the bounding box height of the group will be 65.  The pivot y is at 0 (the centre of the object).  

Is there a reason for this?  My current workaround is to move the group to PosY = 0, get the height and then move the group back.