• 12.7 baseline — 0.6 × season 13.3 (19 gm) + 0.4 × last 10 11.9
• +0.0 opponent leak — they concede 369.9/game vs a 369 league average
• −1.5 at this ground — averages 11.2 there (5 gm)
• vs them: averages 11.7 over 3 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.