• 8.5 baseline — 0.6 × season 8.1 (18 gm) + 0.4 × last 10 9.2
• −0.2 opponent leak — they concede 152.3/game vs a 155.4 league average
• −1.8 at this ground — averages 6.7 there (81 gm)
• vs them: averages 6.0 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.