• 8.8 baseline — 0.6 × season 8.6 (12 gm) + 0.4 × last 10 9.0
• −0.2 opponent leak — they concede 209.2/game vs a 213.6 league average
• −1.2 at this ground — averages 7.6 there (12 gm)
• −3.5 wet forecast — averages 5.2 in the wet (5 gm)
• vs them: averages 7.7 over 6 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.