• 56.6 baseline — 0.6 × season 54.2 (18 gm) + 0.4 × last 10 60.2
• +1.0 opponent leak — they concede 1715.2/game vs a 1686.6 league average
• +12.1 at this ground — averages 68.7 there (6 gm)
• +39.8 wet forecast — averages 96.4 in the wet (7 gm)
• vs them: averages 70.8 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.