• 0.4 baseline — 0.6 × season 0.3 (20 gm) + 0.4 × last 10 0.5
• −0.1 opponent leak — they concede 8.5/game vs a 9.7 league average
• +0.2 at this ground — averages 0.6 there (19 gm)
• vs them: averages 0.9 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 19: 2 — far outside his usual range; kept in the average, not smoothed away.