• 3.9 baseline — 0.6 × season 3.8 (12 gm) + 0.4 × last 10 4.2
• +0.2 opponent leak — they concede 164.6/game vs a 155.4 league average
• −0.6 at this ground — averages 3.3 there (72 gm)
• vs them: averages 3.0 over 5 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.