• 6.2 baseline — 0.6 × season 6.4 (18 gm) + 0.4 × last 10 5.9
• +0.1 opponent leak — they concede 157.2/game vs a 155.4 league average
• −1.0 at this ground — averages 5.2 there (48 gm)
• vs them: averages 6.4 over 9 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.