• 5.0 baseline — 0.6 × season 5.2 (20 gm) + 0.4 × last 10 4.6
• +0.4 opponent leak — they concede 100.5/game vs a 93.4 league average
• +2.5 at this ground — averages 7.5 there (6 gm)
• vs them: averages 7.2 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.