• 12.9 baseline — 0.6 × season 12.9 (7 gm) + 0.4 × last 7 12.9
• +0.0 opponent leak — they concede 213.7/game vs a 213.6 league average

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.