• 16.9 baseline — 0.6 × season 16.4 (20 gm) + 0.4 × last 10 17.6
• −0.6 opponent leak — they concede 150.3/game vs a 155.4 league average
• −1.3 at this ground — averages 15.6 there (86 gm)
• vs them: averages 14.3 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.