• 7.9 baseline — 0.6 × season 7.5 (19 gm) + 0.4 × last 10 8.6
• +0.2 opponent leak — they concede 219.6/game vs a 213.6 league average
• +0.8 at this ground — averages 8.7 there (7 gm)
• vs them: averages 6.3 over 3 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.