• 0.2 baseline — 0.6 × season 0.3 (12 gm) + 0.4 × last 10 0.2
• +0.0 opponent leak — they concede 13.6/game vs a 12.8 league average
• +0.4 at this ground — averages 0.6 there (12 gm)
• −0.2 wet forecast — averages 0 in the wet (5 gm)
• vs them: averages 0.5 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.