• 48.9 baseline — 0.6 × season 47.6 (19 gm) + 0.4 × last 10 50.7
• −6.2 opponent leak — they concede 475.8/game vs a 544.6 league average
• +3.6 at this ground — averages 52.5 there (37 gm)
• vs them: averages 45.3 over 7 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.