• 3.9 baseline — 0.6 × season 3.7 (14 gm) + 0.4 × last 10 4.1
• −0.5 opponent leak — they concede 82.5/game vs a 93.4 league average
• at this ground: too thin to count (3 gm) — shown, adds nothing
• vs them: averages 3.1 over 7 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.