• 5.2 baseline — 0.6 × season 5.3 (14 gm) + 0.4 × last 10 5.0
• −1.6 opponent leak — they concede 16.2/game vs a 23.7 league average
• +2.7 at this ground — averages 7.9 there (57 gm)
• vs them: averages 10.0 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.