• 9.0 baseline — 0.6 × season 8.9 (17 gm) + 0.4 × last 10 9.2
• +0.0 opponent leak — they concede 213.7/game vs a 213.6 league average
• +2.0 at this ground — averages 11 there (4 gm)
• vs them: averages 10.8 over 10 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 18: 17 — far outside his usual range; kept in the average, not smoothed away.