• 12.8 baseline — 0.6 × season 12.4 (16 gm) + 0.4 × last 10 13.5
• +0.1 opponent leak — they concede 156.4/game vs a 155.4 league average
• +1.6 at this ground — averages 14.4 there (38 gm)
• vs them: averages 12.9 over 7 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 18: 5 — far outside his usual range; kept in the average, not smoothed away.