• 18.2 baseline — 0.6 × season 18.9 (17 gm) + 0.4 × last 10 17.1
• −1.2 opponent leak — they concede 322.1/game vs a 344.7 league average
• +10.3 at this ground — averages 28.5 there (4 gm)
• vs them: averages 21.7 over 3 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.