• 13.0 baseline — 0.6 × season 13.9 (20 gm) + 0.4 × last 10 11.7
• −0.0 opponent leak — they concede 212.8/game vs a 213.6 league average
• −1.4 at this ground — averages 11.7 there (6 gm)
• vs them: averages 13.6 over 8 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.