• 3.9 baseline — 0.6 × season 3.8 (17 gm) + 0.4 × last 10 4.1
• −0.1 opponent leak — they concede 207.8/game vs a 213.6 league average
• +1.7 at this ground — averages 5.6 there (41 gm)
• vs them: averages 4.7 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.