• 9.9 baseline — 0.6 × season 10.3 (8 gm) + 0.4 × last 10 9.5
• +0.5 opponent leak — they concede 389.2/game vs a 369 league average
• +2.9 at this ground — averages 12.9 there (7 gm)
• vs them: averages 9.6 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.