If wash from the the motor is reaching that far down then it may be scaring the fish. Had an old timer clean up dock behind me. I would catch one or two and his average was 5 or 6. I ask him what he was doing that I wasn't. His answer he was dropping his anchors to hold position I was using the trolling motor. When I started anchoring my catch percentage per dock went up. Big fish moving around will move some water so there may be some merit to it.