• 18.8 baseline — 0.6 × season 19.1 (15 gm) + 0.4 × last 10 18.3
• −0.5 opponent leak — they concede 207.8/game vs a 213.6 league average
• −1.4 at this ground — averages 17.3 there (80 gm)
• vs them: averages 17.3 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 15: 0 — far outside his usual range; kept in the average, not smoothed away.