• 8.4 baseline — 0.6 × season 8.3 (15 gm) + 0.4 × last 10 8.5
• +0.2 opponent leak — they concede 219.6/game vs a 213.6 league average
• −1.5 at this ground — averages 6.9 there (9 gm)
• vs them: averages 7.1 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.