• 19.3 baseline — 0.6 × season 19.0 (18 gm) + 0.4 × last 10 19.8
• −0.6 opponent leak — they concede 180.6/game vs a 185.9 league average
• +0.4 at this ground — averages 19.7 there (18 gm)
• vs them: averages 17.2 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.