• 8.3 baseline — 0.6 × season 8.2 (9 gm) + 0.4 × last 10 8.4
• +0.7 opponent leak — they concede 399.5/game vs a 369 league average
• +2.4 at this ground — averages 10.7 there (12 gm)
• vs them: averages 13.8 over 4 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.