• 0.2 baseline — 0.6 × season 0.2 (17 gm) + 0.4 × last 10 0.1
• +0.1 opponent leak — they concede 15.8/game vs a 12.2 league average
• +0.7 at this ground — averages 0.9 there (46 gm)
• +0.6 wet forecast — averages 0.8 in the wet (10 gm)
• vs them: averages 0.4 over 5 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.