• 17.0 baseline — 0.6 × season 16.7 (20 gm) + 0.4 × last 10 17.5
• −0.4 opponent leak — they concede 209.2/game vs a 213.6 league average
• −2.6 at this ground — averages 14.4 there (36 gm)
• vs them: averages 15.2 over 6 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.