Send-to-back command on drawings - (Inserting Images)

On production drawings we sometimes insert digital images, or MS Word docs with assembly instructions.

When positioning annotations with the images the note is sometimes covered.

My question is this: Why does the "Send to Back" command sometimes disappear? Does it matter what image type is being used, or is it because of the way it is

inserted into the document? We've noticed it seems to be hit and miss when it shows up, and when it doesn't.

SW 2016

SP 5.0

SolidworksDrawings And Detailing