• 1.0 baseline — 0.6 × season 0.8 (20 gm) + 0.4 × last 10 1.1
• +0.3 opponent leak — they concede 15.8/game vs a 12.2 league average
• −0.0 at this ground — averages 0.9 there (51 gm)
• −0.3 wet forecast — averages 0.6 in the wet (8 gm)
• vs them: averages 1.6 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.