• 7.8 baseline — 0.6 × season 7.4 (20 gm) + 0.4 × last 10 8.3
• +0.3 opponent leak — they concede 160.7/game vs a 155.4 league average
• −2.5 at this ground — averages 5.3 there (58 gm)
• vs them: averages 11.6 over 5 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.