• 17.8 baseline — 0.6 × season 18.2 (20 gm) + 0.4 × last 10 17.3
• +0.5 opponent leak — they concede 378.4/game vs a 369 league average
• +0.3 at this ground — averages 18.1 there (85 gm)
• vs them: averages 20.4 over 8 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.