• 0.2 baseline — 0.6 × season 0.2 (17 gm) + 0.4 × last 10 0.1
• +0.0 opponent leak — they concede 4.5/game vs a 4.2 league average
• +0.6 at this ground — averages 0.8 there (4 gm)
• vs them: averages 0.5 over 2 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.