• 0.3 baseline — 0.6 × season 0.2 (21 gm) + 0.4 × last 10 0.4
• +0.0 opponent leak — they concede 25.8/game vs a 23.7 league average
• +0.5 at this ground — averages 0.8 there (5 gm)
• −0.3 wet forecast — averages 0 in the wet (8 gm)
• vs them: averages 0.4 over 10 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.