• 10.0 baseline — 0.6 × season 10.5 (18 gm) + 0.4 × last 10 9.3
• −0.0 opponent leak — they concede 212.8/game vs a 213.6 league average
• −2.1 at this ground — averages 7.9 there (10 gm)
• vs them: averages 7.4 over 10 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.