• 38.2 baseline — 0.6 × season 44.8 (4 gm) + 0.4 × last 10 28.4
• −1.9 opponent leak — they concede 518.9/game vs a 545.7 league average
• −3.5 wet forecast — averages 34.8 in the wet (8 gm)
• vs them: averages 30.6 over 7 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.