• 91.6 baseline — 0.6 × season 100.2 (16 gm) + 0.4 × last 10 78.8
• −1.3 opponent leak — they concede 1663.5/game vs a 1687.8 league average
• +18.0 at this ground — averages 109.6 there (31 gm)
• vs them: averages 161.8 over 12 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.