If there's any current, it might not be in the cone. Some have posted to drill a hole a little ahead of flow and put transducer there to maintain a reading under those conditions. Even the slightest flow could produce that effect in deeper water. Also, the flutter of spoon, jig, etc. might take it out of the cone which could also produce a negative read... Especially if there's a lot of action. I don't fish that deep, so just sharing others advice.