• 8.7 baseline — 0.6 × season 8.9 (19 gm) + 0.4 × last 10 8.3
• −0.2 opponent leak — they concede 209.2/game vs a 213.6 league average
• −1.4 at this ground — averages 7.3 there (28 gm)
• vs them: averages 8.4 over 5 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: 17 — far outside his usual range; kept in the average, not smoothed away.