• 4.5 baseline — 0.6 × season 4.2 (17 gm) + 0.4 × last 10 4.9
• +0.3 opponent leak — they concede 164.6/game vs a 155.4 league average
• −0.4 at this ground — averages 4.1 there (55 gm)
• vs them: averages 4.0 over 4 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 18: 10 — far outside his usual range; kept in the average, not smoothed away.