• 9.2 baseline — 0.6 × season 8.9 (20 gm) + 0.4 × last 10 9.6
• −0.2 opponent leak — they concede 209.2/game vs a 213.6 league average
• −1.8 at this ground — averages 7.4 there (80 gm)
• vs them: averages 8.5 over 13 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. Round 17: 16 — far outside his usual range; kept in the average, not smoothed away.