• 12.2 baseline — 0.6 × season 12.5 (20 gm) + 0.4 × last 10 11.7
• +0.7 opponent leak — they concede 225.5/game vs a 213.6 league average
• −1.4 at this ground — averages 10.7 there (47 gm)
• vs them: averages 9.6 over 7 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.