• 11.8 baseline — 0.6 × season 11.8 (20 gm) + 0.4 × last 10 11.8
• −0.1 opponent leak — they concede 211.7/game vs a 213.6 league average
• −0.3 at this ground — averages 11.5 there (63 gm)
• vs them: averages 12.9 over 8 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.