You can increase your metal detecting finds on the lower beach by simply using a different search pattern.
If you only search in a straight line along the lower beach, you are box hunting.
Just like using the same control settings on every beach, using the same search pattern will lead to missed treasure hunting opportunities.
The size of your search coil, metal detector sensitivity level, surf washing over the wet sand, type of sand on the lower beach, will all determine the best search pattern to use.
Large search coils and straight line hunting in the splash zone will lead to false signals, especially on the end of each sweep.
Too high a metal detector sensitivity level will also have the same negative effect on your wet sand hunt.
Black sand and straight line searching on the lower beach is made worse by using a large search coil.
I see many local beach hunter's walking down to the lower beach and robotically searching parallel to the water.
They search in straight lines, no matter how high or fast the water is moving over the wet sand, or the size of search coil being used.
Use an East to West directional search pattern on the lower beach, when the conditions say you should.
Avoid box hunting in straight lines on the lower beach to have a chance of finding gold jewelry in the wet sand.
14K gold chain without a pendant, found in the wet sand using a search pattern better suited to the fast water rushing over the lower beach.