• 9.6 baseline — 0.6 × season 9.5 (11 gm) + 0.4 × last 10 9.7
• −0.2 opponent leak — they concede 209.4/game vs a 213.6 league average
• +3.1 at this ground — averages 12.6 there (50 gm)
• vs them: averages 11.8 over 5 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.