• 1.3 baseline — 0.6 × season 1.3 (6 gm) + 0.4 × last 10 1.3
• −0.3 opponent leak — they concede 9.5/game vs a 12.8 league average
• +0.1 at this ground — averages 1.4 there (45 gm)
• vs them: averages 0.4 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 4: 4 — far outside his usual range; kept in the average, not smoothed away.