• 0.4 baseline — 0.6 × season 0.4 (5 gm) + 0.4 × last 10 0.5
• +0.0 opponent leak — they concede 12.8/game vs a 12.8 league average
• +0.2 at this ground — averages 0.6 there (49 gm)
• vs them: averages 1.0 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.