• 10.5 baseline — 0.6 × season 10.2 (17 gm) + 0.4 × last 10 10.9
• −0.2 opponent leak — they concede 210.3/game vs a 213.6 league average
• −3.0 at this ground — averages 7.5 there (66 gm)
• vs them: averages 6.0 over 9 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.