• 12.3 baseline — 0.6 × season 12.6 (8 gm) + 0.4 × last 10 11.7
• −0.2 opponent leak — they concede 364.1/game vs a 369 league average
• −1.9 at this ground — averages 10.3 there (12 gm)
• vs them: averages 16.0 over 2 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.