• 6.2 baseline — 0.6 × season 5.9 (18 gm) + 0.4 × last 10 6.6
• +0.6 opponent leak — they concede 233.1/game vs a 213.6 league average
• +0.6 at this ground — averages 6.8 there (13 gm)
• vs them: averages 6.0 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.