• 6.1 baseline — 0.6 × season 6.2 (20 gm) + 0.4 × last 10 6.1
• +0.6 opponent leak — they concede 233.1/game vs a 213.6 league average
• +2.3 at this ground — averages 8.4 there (41 gm)
• vs them: averages 7.0 over 7 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.