• 8.0 baseline — 0.6 × season 7.7 (18 gm) + 0.4 × last 10 8.3
• −0.3 opponent leak — they concede 150.3/game vs a 155.4 league average
• +0.7 at this ground — averages 8.7 there (97 gm)
• vs them: averages 6.7 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.