• 0.8 baseline — 0.6 × season 0.8 (20 gm) + 0.4 × last 10 0.7
• +0.0 opponent leak — they concede 33.6/game vs a 32.7 league average
• +0.2 at this ground — averages 1 there (61 gm)
• +0.5 wet forecast — averages 1.2 in the wet (14 gm)
• vs them: averages 1.2 over 12 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.