• 10.5 baseline — 0.6 × season 10.4 (20 gm) + 0.4 × last 10 10.7
• +0.3 opponent leak — they concede 377.9/game vs a 369 league average
• +2.3 at this ground — averages 12.8 there (32 gm)
• vs them: averages 8.8 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.