• 15.7 baseline — 0.6 × season 16.1 (20 gm) + 0.4 × last 10 15.2
• −0.8 opponent leak — they concede 203.2/game vs a 213.6 league average
• −1.7 at this ground — averages 14 there (90 gm)
• vs them: averages 11.9 over 8 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.