• 29.7 baseline — 0.6 × season 22.3 (6 gm) + 0.4 × last 10 40.8
• +0.5 opponent leak — they concede 1715.2/game vs a 1686.6 league average
• +40.1 at this ground — averages 69.8 there (5 gm)
• +49.9 wet forecast — averages 79.7 in the wet (6 gm)
• vs them: averages 80.1 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.