• 19.4 baseline — 0.6 × season 20.9 (20 gm) + 0.4 × last 10 17.2
• +0.2 opponent leak — they concede 548.9/game vs a 544.2 league average
• −4.4 at this ground — averages 15 there (4 gm)
• vs them: averages 16.8 over 8 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 4: 59 — far outside his usual range; kept in the average, not smoothed away.