• 0.9 baseline — 0.6 × season 0.9 (16 gm) + 0.4 × last 10 0.9
• +0.1 opponent leak — they concede 61.9/game vs a 56.6 league average
• +0.9 at this ground — averages 1.8 there (6 gm)
• vs them: averages 2.6 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.