• 9.4 baseline — 0.6 × season 9.8 (19 gm) + 0.4 × last 10 8.8
• −0.5 opponent leak — they concede 201.8/game vs a 213.6 league average
• −0.3 at this ground — averages 9.1 there (13 gm)
• vs them: averages 8.0 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.