• 4.1 baseline — 0.6 × season 4.3 (20 gm) + 0.4 × last 10 3.7
• +0.3 opponent leak — they concede 60.4/game vs a 56.6 league average
• +0.0 at this ground — averages 4.1 there (48 gm)
• vs them: averages 3.7 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.