• 0.8 baseline — 0.6 × season 0.6 (20 gm) + 0.4 × last 10 1.0
• +0.2 opponent leak — they concede 12.3/game vs a 9.4 league average
• −0.3 at this ground — averages 0.4 there (18 gm)
• vs them: averages 0.3 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 12: 3 — far outside his usual range; kept in the average, not smoothed away.