• 63.5 baseline — 0.6 × season 55.3 (20 gm) + 0.4 × last 10 76.0
• −6.3 opponent leak — they concede 1519.7/game vs a 1687.8 league average
• +49.5 at this ground — averages 113.1 there (22 gm)
• vs them: averages 109.7 over 10 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.