• 10.5 baseline — 0.6 × season 10.4 (18 gm) + 0.4 × last 10 10.6
• +0.6 opponent leak — they concede 225.5/game vs a 213.6 league average
• −1.3 at this ground — averages 9.2 there (26 gm)
• vs them: averages 8.0 over 3 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.