• 10.6 baseline — 0.6 × season 9.9 (20 gm) + 0.4 × last 10 11.6
• −0.3 opponent leak — they concede 207.8/game vs a 213.6 league average
• +1.2 at this ground — averages 11.8 there (42 gm)
• vs them: averages 11.7 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 20: 19 — far outside his usual range; kept in the average, not smoothed away.