• 3.9 baseline — 0.6 × season 4.0 (15 gm) + 0.4 × last 10 3.7
• +0.0 opponent leak — they concede 155.9/game vs a 155.4 league average
• −0.0 at this ground — averages 3.8 there (24 gm)
• vs them: averages 5.5 over 6 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.