• 8.7 baseline — 0.6 × season 8.9 (17 gm) + 0.4 × last 10 8.4
• −0.0 opponent leak — they concede 154.7/game vs a 155.4 league average
• +0.1 at this ground — averages 8.8 there (6 gm)
• wet forecast: too thin to count (1 gm) — shown, adds nothing
• vs them: averages 7.0 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.