• 10.2 baseline — 0.6 × season 10.5 (15 gm) + 0.4 × last 10 9.9
• +0.7 opponent leak — they concede 368.1/game vs a 344.7 league average
• +1.5 at this ground — averages 11.8 there (37 gm)
• vs them: averages 8.0 over 9 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.