• 2.6 baseline — 0.6 × season 2.4 (20 gm) + 0.4 × last 10 2.8
• −0.5 opponent leak — they concede 9.7/game vs a 12.2 league average
• −0.8 at this ground — averages 1.7 there (46 gm)
• vs them: averages 2.0 over 3 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: 8 — far outside his usual range; kept in the average, not smoothed away.