• 52.0 baseline — 0.6 × season 50.9 (11 gm) + 0.4 × last 10 53.7
• −3.8 opponent leak — they concede 505.5/game vs a 545.7 league average
• −11.9 at this ground — averages 40.2 there (13 gm)
• vs them: averages 38.8 over 5 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.