• 9.4 baseline — 0.6 × season 9.6 (20 gm) + 0.4 × last 10 9.1
• −0.0 opponent leak — they concede 154.7/game vs a 155.4 league average
• −1.0 at this ground — averages 8.4 there (16 gm)
• −6.0 wet forecast — averages 3.4 in the wet (7 gm)
• vs them: averages 7.9 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.