Unfortunately, this is the nature of Adobe Captivate shapes and images.
You can only hope that D&D once will be able to use SVGs as objects. If used as button a SVG is unique because it allows to restrict the hit area to the image instead of the bounding box. To help with this feature request, please log it as well.
This post here discusses a user's requirement to have a drag & drop interaction register sucess only if the drag source is positioned in a specific alignment to the drop target.