Just a few things I have found to be a problem with falsing:
Dirt or sand under coil cover, being a righty, I see my swing lifting coil up on an angle swing to the left, coil control is needed.
Also I have to put elec. tape on shaft and cable the first 12" or so bringing up coil wire straight with no wraps till I get past the first foot then I wrap it around mid shaft. Any loose coil wire hitting branches or just swinging loosely will cause a false.
Also, I tend to have lesche digger on my left hip and carry shovel in left hand, the coil picks up the shovel if I don't hold it behind my back or on my shoulder....maybe I have change in my left pocket...etc....and don't wear steel toe boots....hahaha....
I run sensitvity higher than you...like 27.....and anything that I carry needs to be far enough away so not to pick it up....like at the beach.....at the beach if I am getting false signals, I see it comes from crown cap area, so I disc. out those and falsing is now nulls, and if still bothering me, I will drop gain down from 8 to 7 or 6 if need be. and if it is still bad I will turn off deep.....but I keep sens. up to 27....
you runnin at 16-18 should not be a problem.....so it has got to be one of the above....or something I have not thought of yet....
Good luck Mike....stay out of the hot sun...
