• 54.1 baseline — 0.6 × season 53.6 (9 gm) + 0.4 × last 10 55.0
• +4.8 opponent leak — they concede 1838.8/game vs a 1687.8 league average
• +15.9 at this ground — averages 70 there (9 gm)
• vs them: averages 88.0 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.