• 10.0 baseline — 0.6 × season 10.7 (19 gm) + 0.4 × last 10 8.9
• −0.5 opponent leak — they concede 201.8/game vs a 213.6 league average
• −1.2 at this ground — averages 8.8 there (67 gm)
• vs them: averages 8.9 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.