• 8.4 baseline — 0.6 × season 8.2 (19 gm) + 0.4 × last 10 8.8
• −0.4 opponent leak — they concede 203.2/game vs a 213.6 league average
• −0.7 at this ground — averages 7.7 there (14 gm)
• vs them: averages 7.4 over 5 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.