• 0.9 baseline — 0.6 × season 0.9 (19 gm) + 0.4 × last 10 0.9
• +0.1 opponent leak — they concede 14.7/game vs a 12.8 league average
• +0.6 at this ground — averages 1.5 there (6 gm)
• vs them: averages 1.0 over 7 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.