I set my lowrance sensitive about 72 ,idle boat and the deeper the fish the better the arch,it should arch at 12 to 15 feet good if they come under CENTER of boat. I tilt transducer a little forward for fast speed which hinder a little the coming down side of the arch ,but even then if just right still give full arch,however if clear you do not need full arch. Are you sure those blocks are not bait fish ?