• 9.0 baseline — 0.6 × season 8.9 (20 gm) + 0.4 × last 10 9.2
• +0.3 opponent leak — they concede 219.6/game vs a 213.6 league average
• −3.3 at this ground — averages 5.8 there (9 gm)
• vs them: averages 9.6 over 5 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.