“Recognizing the turning point is vital to successful right angle indicator fishing. Unfortunately, a vast majority of fly anglers who uses poly yarn indicators overlook this critical component. To assist you in understanding the significance of the turning point envision the following two drift examples. Case one: This case begins with the indicator downstream of the fly, and is the most commonly encountered presentation. Because currents are faster on the surface, the indicator drags the fly and the fly very rarely finds the bottom where fish rest and forage. Case two: Here the fly lands downstream of the indicator and indicator must catch up with the fly, so a majority of grabs will go undetected. Hickson and Shubert, who pioneered and coined this technique of nymph fishing, recognized this, and were quick to note that their brightly colored poly yarn indicators would “pivot” and shift colors at the point in the drift when their fly was directly under their indicators. They referred to this pivot as the “turn over” point. Successful indicator fishing stems from achieving the turning point as fast as possible and maintaining this position during the drift through creative and multiple line mends. The result is unsurpassed strike detection even in high, fast water.” (Capital City Weekly by Rich Culver)
The diagram does not really go with the piece by Mr. Culver, but it shows the right angle and poly indicator. Using more than one nymph or having the shot at the very bottom is a different consideration. Query R angle nymphing in Google Images and you can find some more examples.