• 10.9 baseline — 0.6 × season 11.1 (20 gm) + 0.4 × last 10 10.7
• +0.8 opponent leak — they concede 166.4/game vs a 155.4 league average
• −1.5 at this ground — averages 9.4 there (60 gm)
• −0.4 wet forecast — averages 10.5 in the wet (12 gm)
• vs them: averages 12.7 over 9 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.