• 18.3 baseline — 0.6 × season 18.5 (20 gm) + 0.4 × last 10 17.9
• +0.5 opponent leak — they concede 378.4/game vs a 369 league average
• −4.9 at this ground — averages 13.3 there (30 gm)
• vs them: averages 16.3 over 4 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 15: 28 — far outside his usual range; kept in the average, not smoothed away.