• 4.1 baseline — 0.6 × season 4.2 (20 gm) + 0.4 × last 10 3.9
• +0.2 opponent leak — they concede 164/game vs a 155.4 league average
• +0.3 wet forecast — averages 4.4 in the wet (5 gm)

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.