• 59.2 baseline — 0.6 × season 59.6 (13 gm) + 0.4 × last 10 58.7
• −4.8 opponent leak — they concede 1550.3/game vs a 1687.8 league average
• +12.6 at this ground — averages 71.8 there (5 gm)

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.