• 0.9 baseline — 0.6 × season 0.9 (13 gm) + 0.4 × last 10 0.8
• +0.0 opponent leak — they concede 10.2/game vs a 9.7 league average
• −0.4 at this ground — averages 0.5 there (26 gm)
• −0.4 wet forecast — averages 0.4 in the wet (14 gm)
• vs them: averages 1.3 over 4 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.