• 4.0 baseline — 0.6 × season 4.3 (20 gm) + 0.4 × last 10 3.5
• −0.3 opponent leak — they concede 322.1/game vs a 344.7 league average
• +0.2 at this ground — averages 4.2 there (53 gm)
• vs them: averages 3.9 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.