• 3.9 baseline — 0.6 × season 4.0 (17 gm) + 0.4 × last 10 3.8
• +0.7 opponent leak — they concede 108.9/game vs a 93.4 league average
• −0.1 at this ground — averages 3.8 there (44 gm)
• vs them: averages 2.6 over 5 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: 8 — far outside his usual range; kept in the average, not smoothed away.