• 8.4 baseline — 0.6 × season 7.6 (5 gm) + 0.4 × last 10 9.7
• −0.5 opponent leak — they concede 200.3/game vs a 213.6 league average
• +4.3 at this ground — averages 12.7 there (49 gm)
• vs them: averages 14.5 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.