• 8.2 baseline — 0.6 × season 7.9 (17 gm) + 0.4 × last 10 8.7
• −0.2 opponent leak — they concede 209.2/game vs a 213.6 league average
• +0.3 at this ground — averages 8.6 there (9 gm)
• vs them: averages 5.5 over 2 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.