• 3.9 baseline — 0.6 × season 3.8 (9 gm) + 0.4 × last 10 4.2
• −0.0 opponent leak — they concede 92.4/game vs a 92.6 league average
• +1.3 at this ground — averages 5.2 there (32 gm)
• +1.3 wet forecast — averages 5.3 in the wet (4 gm)
• vs them: averages 5.3 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.