• 8.9 baseline — 0.6 × season 8.9 (19 gm) + 0.4 × last 10 8.8
• −0.0 opponent leak — they concede 212.8/game vs a 213.6 league average
• −0.1 at this ground — averages 8.8 there (8 gm)
• vs them: averages 8.8 over 9 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.