• 56.1 baseline — 0.6 × season 55.3 (18 gm) + 0.4 × last 10 57.3
• −3.7 opponent leak — they concede 1576.6/game vs a 1687.8 league average
• +22.5 at this ground — averages 78.5 there (54 gm)
• vs them: averages 46.4 over 13 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.