• 8.1 baseline — 0.6 × season 8.8 (17 gm) + 0.4 × last 10 7.0
• +0.2 opponent leak — they concede 158.8/game vs a 155.4 league average
• +1.8 at this ground — averages 9.9 there (32 gm)
• vs them: averages 9.3 over 7 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.