• 8.4 baseline — 0.6 × season 8.2 (13 gm) + 0.4 × last 10 8.7
• −0.1 opponent leak — they concede 211.2/game vs a 213.6 league average
• +0.5 at this ground — averages 8.9 there (37 gm)
• vs them: averages 6.3 over 8 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 9: 15 — far outside his usual range; kept in the average, not smoothed away.