• 10.4 baseline — 0.6 × season 9.6 (20 gm) + 0.4 × last 10 11.7
• +0.3 opponent leak — they concede 190.8/game vs a 185.9 league average
• −2.4 at this ground — averages 8 there (43 gm)
• −1.3 wet forecast — averages 9.1 in the wet (12 gm)
• vs them: averages 8.7 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.