• 7.8 baseline — 0.6 × season 7.0 (4 gm) + 0.4 × last 10 8.9
• +0.3 opponent leak — they concede 192.6/game vs a 185.9 league average
• +4.2 at this ground — averages 12 there (5 gm)
• vs them: averages 13.7 over 3 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.