Really great writing, Jeff. Both informative and entertaining. Kudos.
Maybe the problem some are experiencing is that the designations are confusing (blame Apple rather than iFixit). the P2 is also known as PL1. The P5 is also known as PL4. The P6 is also known as PL5. So it is possible to mistake the P6 (PL5) for the P5 (PL4), meaning it (P6-PL5) will be too big, while the P5 (PL4) will be just right. Sort of a 3 Bears explanation, but it is very confusing.