• 19.1 baseline — 0.6 × season 19.1 (10 gm) + 0.4 × last 10 19.1
• +0.9 opponent leak — they concede 386.2/game vs a 369 league average
• −2.0 at this ground — averages 17.1 there (50 gm)
• vs them: averages 21.7 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.