I assume in both scenarios you’ll be ending up with metal between the tag and the reader, so it’s a no-go.
slightly oversimplified rule of thumb:
- metal between reader and tag will “block” the radio field, forcing the field to bend around it. the closer you are on the other side the less of the field you get. So a larger antenna and more distance from the metallic body might help… or the loss of energy might still be too much.
- metal behind the tag may “reflect” some of the radio field causing interference. tags must be shielded in a special way (i.e. not cheapy tags) to allow for that.
- metal in direct contact with the tag might “sap/ground” some of the energy being harvested, rendering the tag starving.
So you want it placed:
- with something non metallic between the tag and the metal
- not surrounded by metal like a satellite dish effect
- not having metal between the tag and the reader