• 8.2 baseline — 0.6 × season 7.5 (15 gm) + 0.4 × last 10 9.2
• +0.4 opponent leak — they concede 224.7/game vs a 213.6 league average
• +0.5 at this ground — averages 8.7 there (19 gm)
• vs them: averages 8.0 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.