• 4.1 baseline — 0.6 × season 4.4 (18 gm) + 0.4 × last 10 3.7
• +1.1 opponent leak — they concede 117.8/game vs a 93.4 league average
• −0.8 at this ground — averages 3.4 there (20 gm)
• −3.0 wet forecast — averages 1.1 in the wet (7 gm)
• vs them: averages 2.2 over 5 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.