• 4.2 baseline — 0.6 × season 3.9 (17 gm) + 0.4 × last 10 4.8
• −0.2 opponent leak — they concede 88/game vs a 93.4 league average
• −0.4 at this ground — averages 3.9 there (8 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 9: 10 — far outside his usual range; kept in the average, not smoothed away.