• 14.1 baseline — 0.6 × season 14.6 (20 gm) + 0.4 × last 10 13.4
• +0.4 opponent leak — they concede 219.6/game vs a 213.6 league average
• −2.9 at this ground — averages 11.2 there (17 gm)
• vs them: averages 14.3 over 9 games — evidence, never summed

Derived, not measured — plain arithmetic over his real games, shown in full. Adjustments can overlap (a game at this ground can also be a wet one); they add simply, and this note is the admission.