• 5.7 baseline — 0.6 × season 5.9 (17 gm) + 0.4 × last 10 5.5
• +0.5 opponent leak — they concede 233.1/game vs a 213.6 league average
• +1.8 at this ground — averages 7.5 there (41 gm)
• vs them: averages 5.3 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.