• 9.0 baseline — 0.6 × season 9.3 (8 gm) + 0.4 × last 10 8.6
• −0.1 opponent leak — they concede 211.2/game vs a 213.6 league average
• +4.0 at this ground — averages 13 there (6 gm)
• vs them: averages 12.0 over 8 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.