They were pretty clear in the report that this is because the M4 is incredibly overgassed paired with the OCM5 being a really super high backpressure can, and kept reiterating that this metric should improve drastically with tuning, making it's overall metric even more impressive since it's basically being handicapped by the platform it was tested on.

Hell, even take tuning out of the equation. Once you've heard enough cans you begin to see that the at-the-ear metric has increasingly limited utility when not shooting in a free-field environment, i.e. anywhere with reflective surfaces which Pew Science actually covered here where a HUXWRX FLOW 556k is actually more hazardous to the shooter than an RC2 despite having a 139% better ear rating in free-field.

Couple that with actually tuning the gas port on the host as Pew did here vs here where the at-ear rating increased 47% on the same can and host just by shrinking the gas port diameter and it's clear that something like the OCM5 would benefit a lot from this which Jay even says and reiterates ad nauseum in the OCM5 report. Also notice how the ear rating is being weighted in all these reports, despite going from a 22.0 to a 32.5 on these Maxim DSX tests, the overall rating only increased 1.0 point, pretty indicative of how important Pew themselves sees the at-ear metric.

TL;DR: The ear rating is a metric with limited utility you're using wrong.