• 10.9 baseline — 0.6 × season 10.5 (17 gm) + 0.4 × last 10 11.6
• +0.0 opponent leak — they concede 213.7/game vs a 213.6 league average
• −2.3 wet forecast — averages 8.6 in the wet (16 gm)
• vs them: averages 10.2 over 11 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.