In a conventional straight-line overhead presentation, a near-straight rod tip path supports a straight fly leg and a narrow loop. A convex path tends to produce a convex fly leg and a wider loop. A concave path can produce a tail, though a dip alone is not the whole story.

The rod tip path during the casting stroke shapes the fly leg of the loop. Match the casting arc to how much the rod bends, and the tip travels near-straight — that is the narrow loop you want most of the time.

• Narrow loop — near-straight. The arc matches the rod bend, so the tip path is close to a straight line and the fly leg is straight.
• Wide loop — convex. The arc is wider than the bend needs, so the tip wanders up and over in a dome shape and the fly leg curves upward.
• Tailing loop — concave. The arc is too narrow for the bend, or force was applied unevenly, so the tip path dips into a concave shape instead of staying straight. The fly leg dips and crosses the rod leg; that crossing is what makes it a tail.

Read the fly leg and you know which path you made: straight, curving up, or curving down and across.

Source

From the CI Study Guide (2025) (PDF), Bruce Richards’ Five Essentials and Task 16 loop shapes; terms from the FFI Fly Casting Definitions.