• 0.9 baseline — 0.6 × season 0.9 (19 gm) + 0.4 × last 10 0.8
• +0.0 opponent leak — they concede 13.4/game vs a 12.8 league average
• +0.4 at this ground — averages 1.3 there (68 gm)
• vs them: averages 1.3 over 8 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.