• 3.2 baseline — 0.6 × season 3.3 (20 gm) + 0.4 × last 10 3.2
• +0.3 opponent leak — they concede 13.5/game vs a 12.2 league average
• −1.0 at this ground — averages 2.2 there (9 gm)
• vs them: averages 3.6 over 5 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.