• 4.8 baseline — 0.6 × season 4.8 (20 gm) + 0.4 × last 10 4.8
• +0.4 opponent leak — they concede 100.5/game vs a 93.4 league average
• −1.8 at this ground — averages 3 there (9 gm)
• vs them: averages 3.2 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.