• 3.9 baseline — 0.6 × season 3.8 (19 gm) + 0.4 × last 10 4.0
• +0.0 opponent leak — they concede 94/game vs a 93.4 league average
• +1.3 at this ground — averages 5.1 there (8 gm)
• vs them: averages 4.7 over 9 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.