• 13.8 baseline — 0.6 × season 14.3 (18 gm) + 0.4 × last 10 13.1
• +0.0 opponent leak — they concede 369.9/game vs a 369 league average
• −0.9 at this ground — averages 13 there (48 gm)
• vs them: averages 14.9 over 9 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.