• 0.8 baseline — 0.6 × season 0.8 (20 gm) + 0.4 × last 10 0.6
• +0.1 opponent leak — they concede 4.5/game vs a 4.1 league average
• −0.5 at this ground — averages 0.3 there (4 gm)
• +0.0 wet forecast — averages 0.8 in the wet (12 gm)
• vs them: averages 0.8 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.