The Gravel Bed of the New Septic System is Settling. Problem?

Today when I went out to the porch to check the temperature and looked down to the Septic Gravel Bed I felt that it had settled some more. I find it strange that it is just in this one spot. We had left a message for Clement Rose Excavating Inc. who was the installer of the New Septic System (hired by the previous owner) to find out whether this is a problem or whether we simply need to add more gravel, but no answer. I guess we have to chase him down...Does anybody know perhaps?