• 57.4 baseline — 0.6 × season 54.9 (20 gm) + 0.4 × last 10 61.1
• −1.2 opponent leak — they concede 1652.5/game vs a 1687.8 league average
• +23.8 at this ground — averages 81.2 there (49 gm)
• vs them: averages 72.0 over 2 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.