• 13.3 baseline — 0.6 × season 14.1 (19 gm) + 0.4 × last 10 12.1
• −1.9 opponent leak — they concede 466.4/game vs a 545.7 league average
• +5.0 at this ground — averages 18.3 there (4 gm)
• vs them: averages 15.9 over 9 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.