• 20.3 baseline — 0.6 × season 20.6 (16 gm) + 0.4 × last 10 19.8
• +0.4 opponent leak — they concede 351.7/game vs a 344.7 league average
• +1.6 at this ground — averages 21.9 there (26 gm)
• vs them: averages 13.6 over 7 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 23: 0 — far outside his usual range; kept in the average, not smoothed away.