• 20.9 baseline — 0.6 × season 22.4 (14 gm) + 0.4 × last 10 18.7
• +1.4 opponent leak — they concede 368.1/game vs a 344.7 league average
• +18.4 at this ground — averages 39.3 there (4 gm)
• vs them: averages 38.8 over 6 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 1: 44 — far outside his usual range; kept in the average, not smoothed away.