• 8.7 baseline — 0.6 × season 9.1 (9 gm) + 0.4 × last 10 8.2
• +0.4 opponent leak — they concede 386.2/game vs a 369 league average
• −0.4 at this ground — averages 8.4 there (26 gm)
• vs them: averages 13.7 over 3 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 11: 21 — far outside his usual range; kept in the average, not smoothed away.