This one is really weird. I draw a shape in Illustrator save it. Import into an InDesign box, size it proportionally to the box, then fit box to image. BUT, there some inset usually on two or three sides ?! I can see that the inset is caused by the InDesign bounding box for the shape not being tight and ID uses it's bounding box to fit the picture box, but I don't know why it is doing this. When I test this using a standard shape like an elipse it is OK, sometimes it is OK for a shape I draw, quite often the inset is inconsistent.