• 4.2 baseline — 0.6 × season 4.4 (7 gm) + 0.4 × last 10 3.8
• +0.6 opponent leak — they concede 64.2/game vs a 56.6 league average
• −1.8 at this ground — averages 2.4 there (5 gm)
• vs them: averages 2.7 over 3 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.