• 6.8 baseline — 0.6 × season 6.8 (20 gm) + 0.4 × last 10 7.0
• −0.8 opponent leak — they concede 82.5/game vs a 93.4 league average
• −2.1 at this ground — averages 4.8 there (34 gm)
• vs them: averages 4.9 over 10 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.