Another way to look at the problem is to check how evenly the sail luffs as you head up when sailing close-hauled. When the tension on the leech allows it to twist open properly, the sail will luff almost simultaneously at every height along the leading edge. If the top telltale luffs more than a split second before the bottom, the lead may be too far aft. The top of the sail should luff a little before the bottom. Move the lead forward to pull down on the clew, increasing leech tension and reducing twist. If the bottom of the sail luffs first, move the lead aft. This eases the tension on the leech, allowing the clew to rise and increasing twist.