• 3.9 baseline — 0.6 × season 3.8 (16 gm) + 0.4 × last 10 4.0
• −1.4 opponent leak — they concede 15.1/game vs a 23.7 league average
• at this ground: too thin to count (2 gm) — shown, adds nothing
• vs them: averages 1.3 over 3 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.