• 4.1 baseline — 0.6 × season 4.0 (14 gm) + 0.4 × last 10 4.3
• −0.6 opponent leak — they concede 80.8/game vs a 93.4 league average
• −2.1 at this ground — averages 2 there (4 gm)
• −1.3 wet forecast — averages 2.8 in the wet (6 gm)
• vs them: averages 2.7 over 3 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.