• 10.2 baseline — 0.6 × season 9.7 (15 gm) + 0.4 × last 10 10.9
• +0.9 opponent leak — they concede 233.1/game vs a 213.6 league average
• −2.9 at this ground — averages 7.3 there (10 gm)
• vs them: averages 5.0 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.