• 5.6 baseline — 0.6 × season 5.5 (20 gm) + 0.4 × last 10 5.8
• +0.4 opponent leak — they concede 100.5/game vs a 93.4 league average
• −1.7 at this ground — averages 3.9 there (97 gm)
• vs them: averages 3.8 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.