Then I thought maybe it exists to protect the windscreen from the boom accidentally impacting it. But upon further contemplation, that seemed like an odd requirement as other aircraft have their receptacles in somewhat sensitive places and they don't have similar deflection systems.

Frustrated, I reached out to a veteran boom operator contact of mine for answers and answers I received! It turns out that the system in question exists for aerodynamic and flight control purposes—it was a spoiler. Knowing that, I was able to find the NATO air-to-air refueling manual online, which discusses each aircraft's unique issues when it comes to tanking.