• 19.1 baseline — 0.6 × season 19.5 (17 gm) + 0.4 × last 10 18.6
• −0.3 opponent leak — they concede 364.1/game vs a 369 league average
• −7.2 at this ground — averages 11.9 there (66 gm)
• vs them: averages 10.6 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.