• 19.4 baseline — 0.6 × season 19.8 (20 gm) + 0.4 × last 10 19.0
• +0.4 opponent leak — they concede 375.7/game vs a 369 league average
• −2.7 at this ground — averages 16.7 there (32 gm)
• vs them: averages 15.2 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.