• 7.9 baseline — 0.6 × season 7.7 (17 gm) + 0.4 × last 10 8.1
• −0.5 opponent leak — they concede 87/game vs a 93.4 league average
• −1.1 at this ground — averages 6.8 there (87 gm)
• vs them: averages 8.2 over 12 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.