• 99.6 baseline — 0.6 × season 100.2 (17 gm) + 0.4 × last 10 98.7
• −9.9 opponent leak — they concede 1519.7/game vs a 1687.8 league average
• +3.4 at this ground — averages 103 there (20 gm)
• vs them: averages 112.6 over 8 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.