• 9.0 baseline — 0.6 × season 9.0 (7 gm) + 0.4 × last 10 9.1
• +0.1 opponent leak — they concede 156.4/game vs a 155.4 league average
• −0.5 at this ground — averages 8.5 there (38 gm)
• vs them: averages 8.3 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.