• 12.4 baseline — 0.6 × season 12.2 (12 gm) + 0.4 × last 10 12.8
• −0.2 opponent leak — they concede 363.9/game vs a 369 league average
• −0.0 at this ground — averages 12.4 there (45 gm)
• vs them: averages 10.4 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.