• 1.0 baseline — 0.6 × season 1.1 (13 gm) + 0.4 × last 10 0.8
• +0.1 opponent leak — they concede 64.3/game vs a 56.6 league average
• +0.4 at this ground — averages 1.3 there (40 gm)
• vs them: averages 0.9 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.