• 1.0 baseline — 0.6 × season 0.9 (20 gm) + 0.4 × last 10 1.0
• +0.1 opponent leak — they concede 38.4/game vs a 35.7 league average
• +3.1 at this ground — averages 4.1 there (34 gm)
• vs them: averages 4.5 over 10 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: 4 — far outside his usual range; kept in the average, not smoothed away.