• 3.7 baseline — 0.6 × season 3.6 (17 gm) + 0.4 × last 10 3.9
• +0.2 opponent leak — they concede 34.4/game vs a 32.8 league average
• +0.1 at this ground — averages 3.8 there (64 gm)
• vs them: averages 3.3 over 6 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 20: 10 — far outside his usual range; kept in the average, not smoothed away.