• 4.8 baseline — 0.6 × season 4.8 (10 gm) + 0.4 × last 10 4.8
• +0.5 opponent leak — they concede 104/game vs a 93.4 league average
• +0.2 at this ground — averages 5 there (45 gm)
• vs them: averages 5.6 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.