Fish hawk x4 d discrepancy

[Lily 2]

Questions concerning true depth fish fish hawk.   My trudepth often times doesn't line up with what is displayed on my fish finder by some times feet.   For example if I set my downrigger to 40 feet my fish hawk will read 50 ft true depth and my fish finder will read the weight at say 35 ft.  My blow back would answer the question for the weight reading 35 feet on the sonar but how is it possible for my true depth on the fish hawk to be further than the amount of cable that I have out.   Is there a way to calibrate the fish hawk my riggers are zeroed at the water line.  It can be frustrating when wou are fishing out side of the sonar cone to be getting fish hawk readings that physically aren't possible.   Anyone else experience this kind of issue.  All of the other aspects of the fish hawk work fine as far as speed and temp