• 1.0 baseline — 0.6 × season 0.9 (13 gm) + 0.4 × last 10 1.1
• −0.4 opponent leak — they concede 2.6/game vs a 4.2 league average
• −0.3 at this ground — averages 0.7 there (6 gm)
• vs them: averages 0.5 over 10 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 19: 3 — far outside his usual range; kept in the average, not smoothed away.