I have a 12” HDS live unit. I only use the mapping that was already installed in the unit. When I pull up to the bank to mark brush piles or stumps the map shows me way off the bank. I fish Cherokee and Douglas lake and both are drawn way down in the winter. Do the maps only show depths and contours at full pool? I also noticed the river channels didn’t seem accurate either. Is this normal or do I have something set wrong? Thanks.