• 12.5 baseline — 0.6 × season 12.6 (17 gm) + 0.4 × last 10 12.3
• +0.3 opponent leak — they concede 377.9/game vs a 369 league average
• −0.3 at this ground — averages 12.2 there (67 gm)
• vs them: averages 11.3 over 9 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.