• 18.3 baseline — 0.6 × season 17.6 (19 gm) + 0.4 × last 10 19.4
• +0.0 opponent leak — they concede 369.9/game vs a 369 league average
• −4.4 at this ground — averages 13.9 there (8 gm)
• vs them: averages 15.1 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.