Using the information you provide, I looked up "myDoc.Shapes.AddPictures" using Google. Picking the top return (microsoft.docs sounds like a winner):
Shapes.AddPicture method (Excel) | Microsoft Docs[
^]
At the end of the post I see what could be the EXACT solution you're looking for: by explicitly placing the "Shape" at the coordinates one should be able to customize some default placement.
Since we don't really know what interface to VB you've got running, it's hard to describe an easier way. Typically more information is available to a user of VisualStudio, or in Excel in the Visual Basic for Applications IDE; it's probably the same interface used by Word. You can usually access positions of controls in either case by opening the Properties window. At least this has been my experience.