When you lengthen a forward elbow cast, you take the rod back further, and the motion is very much like the spear chucker. In fact, if you read Kyte's description, he says it is a throwing motion like a baseball pitcher.
"I start a beginning class with what I call the “ebow-forward” style. At the start of the forward cast, your elbow is directly below your hand, which is at ear level and slightly forward of your casting shoulder (Figure 1).
It is part of an overhand baseball throw, which is called a “kinetic whip” because each body part moves in a whip-like sequence, adding to the overall force."
I think you are confusing the beginner's elbow forward cast with an advanced elbow forward cast. In the longer casts as in the images above, the elbow is taken back but it is not taken back sidearm like Lefty Kreh's Style. The casting hand is still ABOVE and not below the shoulder.
The arm is extended backward in order to increase the stroke length that is needed for a longer cast. See the stop motion photos of Steve and Joan. Is the hand above or below the shoulder?
The direction of the stroke also changes so it is not angled down but forward so the stroke is forward and not down. These are all adaptations of the elbow forward style of casting for longer casts.
Notice that the spear chucker has his hand ABOVE the shoulder and the spear is ABOVE his shoulder. The motion of the spear checker is a elbow forward motion with a longer stoke because he is throwing the spear as far as he can.
His spear is NOT along his side with the elbow low and the throwing hand BELOW the shoulder as it would be with the low elbow style of Lefty Kreh.
See a slow motion of Lefty casting. Is Lefty's hand above or BELOW his shoulder?
The casting motion of Lefty's low elbow style is the exact opposite of the elbow forward style.
Al Kyte had both casting motions analyzed byCraig Johnson, a fly caster and professor of biomechanics. Here is how the casting motions differ.
"To understand this (low elbow) style better, I recently spent time with professor Craig Johnson, who teaches both biomechanics and fly casting at Saint Mary’s College, in Moraga [California]. We discovered that this shoulder movement, though occurring in a diagonal, rather than vertical plane, is opposite to that used by elbow-forward casters. In the elbow-forward style, you start with shoulder flexion (lifting the elbow in front) on the back cast, then shoulder extension (lowering the elbow) on the forward cast. This order is reversed in the low-elbow style, where you sort with shoulder extension (moving the “low” elbow back) on the back cast, then shoulder flexion; (moving the elbow forward) on the forward cast. We were fascinated to learn that the same body part can be moved in the opposite direction, using directly opposing muscle groups, yet produce the identical effect an overhead cast."