• 49.5 baseline — 0.6 × season 51.8 (12 gm) + 0.4 × last 10 46.1
• −4.0 opponent leak — they concede 1550.3/game vs a 1687.8 league average
• +13.6 at this ground — averages 63.1 there (9 gm)
• vs them: averages 77.5 over 4 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.