• 0.6 baseline — 0.6 × season 0.8 (16 gm) + 0.4 × last 10 0.4
• +0.1 opponent leak — they concede 3.9/game vs a 3.5 league average
• +0.1 at this ground — averages 0.7 there (12 gm)
• vs them: averages 0.6 over 5 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.