• 7.5 baseline — 0.6 × season 7.5 (20 gm) + 0.4 × last 10 7.7
• +0.2 opponent leak — they concede 219.2/game vs a 213.6 league average
• +2.2 at this ground — averages 9.8 there (32 gm)
• vs them: averages 6.2 over 6 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.