• 12.0 baseline — 0.6 × season 12.2 (5 gm) + 0.4 × last 10 11.6
• +0.2 opponent leak — they concede 375.7/game vs a 369 league average
• −2.4 at this ground — averages 9.6 there (17 gm)
• vs them: averages 15.0 over 1 game — 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.