Detail Callout Boundary Coordinates

Take a look at the following screenshot:

This is a drawing model which contains a detail callout of the design model. I'm trying to get the callout rectangle coordinates programatically. The callout is a reference into the design model but if I retrieve the reference bounding box I get the "photo corners" rectangle rather than the callout rectangle. 

Why is the reference boundary offset from the callout? 

Are there more efficient methods to get the callout boundary coordinates?