• 3.9 baseline — 0.6 × season 3.9 (10 gm) + 0.4 × last 10 3.9
• +0.3 opponent leak — they concede 38/game vs a 35.7 league average
• −1.8 at this ground — averages 2.1 there (12 gm)
• wet forecast: too thin to count (3 gm) — shown, adds nothing
• vs them: averages 1.9 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.