• 11.8 baseline — 0.6 × season 11.3 (20 gm) + 0.4 × last 10 12.5
• −0.0 opponent leak — they concede 212.8/game vs a 213.6 league average
• +0.4 at this ground — averages 12.2 there (10 gm)
• vs them: averages 10.0 over 10 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.