• 0.6 baseline — 0.6 × season 0.5 (15 gm) + 0.4 × last 10 0.6
• −0.1 opponent leak — they concede 3.7/game vs a 4.1 league average
• −0.1 at this ground — averages 0.5 there (4 gm)
• vs them: averages 0.2 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 17: 2 — far outside his usual range; kept in the average, not smoothed away.