• 6.0 baseline — 0.6 × season 6.1 (9 gm) + 0.4 × last 10 5.9
• −0.9 opponent leak — they concede 30.1/game vs a 35.3 league average
• +0.6 at this ground — averages 6.6 there (43 gm)
• vs them: averages 4.2 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.