• 8.9 baseline — 0.6 × season 9.0 (9 gm) + 0.4 × last 10 8.8
• +0.0 opponent leak — they concede 213.7/game vs a 213.6 league average
• wet forecast: too thin to count (2 gm) — shown, adds nothing
• vs them: averages 9.0 over 4 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.