• 0.2 baseline — 0.6 × season 0.2 (20 gm) + 0.4 × last 10 0.3
• −0.1 opponent leak — they concede 2.6/game vs a 4.1 league average
• −0.1 at this ground — averages 0.1 there (17 gm)
• vs them: averages 0.5 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.