• 19.5 baseline — 0.6 × season 19.7 (16 gm) + 0.4 × last 10 19.2
• +0.9 opponent leak — they concede 386.5/game vs a 369 league average
• −1.8 at this ground — averages 17.7 there (18 gm)
• vs them: averages 13.5 over 2 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.