• 8.9 baseline — 0.6 × season 8.4 (17 gm) + 0.4 × last 10 9.7
• −0.6 opponent leak — they concede 145.2/game vs a 155.4 league average
• −1.8 at this ground — averages 7.2 there (6 gm)
• vs them: averages 5.4 over 7 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 13: 18 — far outside his usual range; kept in the average, not smoothed away.