• 8.5 baseline — 0.6 × season 8.1 (16 gm) + 0.4 × last 10 9.2
• +0.5 opponent leak — they concede 164.6/game vs a 155.4 league average
• −3.4 at this ground — averages 5.1 there (11 gm)
• vs them: averages 6.9 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.