• 19.1 baseline — 0.6 × season 19.1 (19 gm) + 0.4 × last 10 19.2
• −0.9 opponent leak — they concede 203.2/game vs a 213.6 league average
• −2.8 at this ground — averages 16.3 there (71 gm)
• vs them: averages 13.7 over 7 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.