• 0.9 baseline — 0.6 × season 0.8 (19 gm) + 0.4 × last 10 1.1
• +0.0 opponent leak — they concede 12.8/game vs a 12.8 league average
• +0.2 at this ground — averages 1.1 there (52 gm)
• vs them: averages 1.8 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.