• 10.6 baseline — 0.6 × season 10.6 (20 gm) + 0.4 × last 10 10.6
• +0.1 opponent leak — they concede 157.2/game vs a 155.4 league average
• −4.4 at this ground — averages 6.2 there (9 gm)
• vs them: averages 8.5 over 8 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.