• 3.8 baseline — 0.6 × season 3.7 (18 gm) + 0.4 × last 10 4.0
• −0.3 opponent leak — they concede 87/game vs a 93.4 league average
• +1.5 at this ground — averages 5.3 there (16 gm)
• +0.5 wet forecast — averages 4.3 in the wet (8 gm)
• vs them: averages 3.3 over 9 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.