• 41.0 baseline — 0.6 × season 40.9 (20 gm) + 0.4 × last 10 41.1
• +0.7 opponent leak — they concede 1715.2/game vs a 1686.6 league average
• +15.0 at this ground — averages 56 there (4 gm)
• −12.0 wet forecast — averages 29 in the wet (5 gm)
• vs them: averages 47.5 over 8 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.