• 13.2 baseline — 0.6 × season 13.2 (20 gm) + 0.4 × last 10 13.1
• +0.3 opponent leak — they concede 378.4/game vs a 369 league average
• −4.0 at this ground — averages 9.1 there (9 gm)
• vs them: averages 13.6 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.