• 10.5 baseline — 0.6 × season 10.2 (18 gm) + 0.4 × last 10 10.8
• +0.3 opponent leak — they concede 219.2/game vs a 213.6 league average
• −2.7 at this ground — averages 7.7 there (51 gm)
• vs them: averages 11.2 over 6 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.