• 39.5 baseline — 0.6 × season 40.4 (16 gm) + 0.4 × last 10 38.1
• +0.1 opponent leak — they concede 345.7/game vs a 344.9 league average
• +9.7 at this ground — averages 49.2 there (6 gm)
• −4.0 wet forecast — averages 35.4 in the wet (9 gm)
• vs them: averages 42.3 over 11 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.