It would be good to see a normal sized mintmark next to the one in question. If they are both the same overall size, then coin contact may have altered your coin. The angle of light can make something appear differently than it really is at a different angle. In order for a RPM to listed, it must show a spread between the punching. Well all mintmarks are struck more than once. It just that some are punch in a different location that makes the differences. Thus a spread is formed on the mintmark. On your coin a slight glace blow to the coin may have altered the west edge of the mintmark. Thus creating the shadow you are looking at. But comparing the images to another coin, may show they are the same size. The RPMs size will be be enlarged. Thus indicating a spread between punching. So far, we are seeing what you are showing us, but is the mintmark enlarged, or or normal in size?