• 11.1 baseline — 0.6 × season 11.6 (20 gm) + 0.4 × last 10 10.4
• −0.2 opponent leak — they concede 209.2/game vs a 213.6 league average
• +1.1 at this ground — averages 12.2 there (21 gm)
• vs them: averages 11.3 over 4 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 21: 3 — far outside his usual range; kept in the average, not smoothed away.